chore: move business tooling out of the public library; tidy filestore naming

Keep the public tree project-generic. Business/one-off tools, deployment
and business docs move to the private oo-workspace repo.

Moved to oo-workspace:
- cmd/ooscan, cmd/pdfamount, cmd/kontoblatt, cmd/kontolink
- internal/xlspipe (cutover-portugal workbook) -> oow workbook build
  (drops the --template/--title flags from oo docs put-xlsx)
- deploy/docker-compose.rclone-webdav.yml + docs/rclone-webdav.md
- docs/crm-associations.md

Removed GitHub-era leftovers:
- .github/workflows/release-please.yml, release-please-config.json,
  .release-please-manifest.json (tags are created on Gitea per SemVer)

Naming: the FileStore subsystem is now filestore_*.go (was file_*.go) to
match files_*.go (project Documents). Docs/AGENTS/README updated.

filestore_core.go

@@ -0,0 +1,262 @@
+package onlyoffice
+
+// Canonical file model and the backend-agnostic store interface. REST
+// (files.go), WebDAV (files_webdav.go) and future backends (PostgreSQL,
+// Elasticsearch) implement FileStore/Searcher so callers stop depending on a
+// concrete transport. This file holds only types and pure conversions — no IO.
+
+import (
+	"context"
+	"io"
+	"mime"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Kind distinguishes files from folders in the canonical model.
+type Kind int
+
+const (
+	File Kind = iota
+	Folder
+)
+
+// String renders the kind for logs and table output.
+func (k Kind) String() string {
+	switch k {
+	case File:
+		return "file"
+	case Folder:
+		return "folder"
+	default:
+		return "unknown"
+	}
+}
+
+// Provider names for the FileStore adapters.
+const (
+	ProviderREST = "rest"
+	ProviderDAV  = "dav"
+)
+
+// Entry is the backend-independent representation of a document or folder.
+// Fields that a backend cannot supply stay at their zero value.
+type Entry struct {
+	ID       string
+	ParentID string
+	Title    string
+	Kind     Kind
+	Size     int64
+	MIME     string
+	Created  time.Time
+	Modified time.Time
+	// Updated is the backend-native timestamp string, when the backend exposes
+	// one. It lets list output round-trip the API value; Modified is the
+	// parsed form for logic.
+	Updated  string
+	Version  int
+	Provider string
+
+	// Folder-only counters. Zero for files and for backends that do not
+	// report them.
+	FilesCount   int
+	FoldersCount int
+}
+
+// FileStore is the operation surface every file backend implements.
+type FileStore interface {
+	Name() string
+	List(ctx context.Context, parentID string) ([]Entry, error)
+	Stat(ctx context.Context, id string) (Entry, error)
+	CreateFolder(ctx context.Context, parentID, title string) (Entry, error)
+	Upload(ctx context.Context, parentID, title string, r io.Reader) (Entry, error)
+	Download(ctx context.Context, id string, w io.Writer) (int64, error)
+	Move(ctx context.Context, ids []string, parentID string) error
+	Copy(ctx context.Context, ids []string, parentID string) error
+	Rename(ctx context.Context, id, title string) error
+	Delete(ctx context.Context, ids []string) error
+}
+
+// SearchQuery narrows a Searcher request. InContent asks the backend to match
+// document bodies, not just titles. Substring switches title matching from the
+// analyzer's whole-token match to a case-insensitive "*term*" wildcard and ANDs
+// every whitespace-separated term (e.g. "rechnung 2025").
+type SearchQuery struct {
+	Text       string
+	InContent  bool
+	FolderID   string
+	Extensions []string
+	Limit      int
+	Substring  bool
+}
+
+// SearchHit is one Searcher result: the matching entry plus backend-specific
+// ranking metadata.
+type SearchHit struct {
+	Entry
+	Score     float64
+	Highlight string
+	Path      []string
+}
+
+// Searcher is the optional content/name search surface. Only some backends
+// (for example Elasticsearch) provide it.
+type Searcher interface {
+	Search(ctx context.Context, q SearchQuery) ([]SearchHit, error)
+	Name() string
+}
+
+// FileStore returns the adapter for a backend name: ProviderREST (default),
+// ProviderDAV (alias "webdav") or the read-only SQL store (ProviderPG,
+// ProviderMySQL and the aliases "pg"/"sql"). The SQL store is opened from the
+// environment (ONLYOFFICE_DSN / ONLYOFFICE_PG_*); when it cannot be opened the
+// returned store surfaces that error on every operation instead of returning
+// nil. Use SQLFileStore when the open error itself is needed. Unknown or empty
+// names select the REST backend. The composed facade (backend
+// selection/fallback) lives on FileClient in filestore_facade.go.
+func (c *Client) FileStore(backend string) FileStore {
+	switch strings.ToLower(strings.TrimSpace(backend)) {
+	case ProviderDAV, "webdav":
+		return &davStore{c: c}
+	case ProviderPG, ProviderMySQL, "pg", "sql":
+		s, err := c.SQLFileStore()
+		if err != nil {
+			return &errStore{name: strings.ToLower(strings.TrimSpace(backend)), err: err}
+		}
+		return s
+	default:
+		return &restStore{c: c}
+	}
+}
+
+// errStore is the FileStore placeholder returned when a backend cannot be
+// opened (for example SQL without a DSN). Every operation returns the recorded
+// error instead of panicking on a nil interface.
+type errStore struct {
+	name string
+	err  error
+}
+
+func (s *errStore) Name() string { return s.name }
+
+func (s *errStore) List(context.Context, string) ([]Entry, error) { return nil, s.err }
+
+func (s *errStore) Stat(context.Context, string) (Entry, error) { return Entry{}, s.err }
+
+func (s *errStore) CreateFolder(context.Context, string, string) (Entry, error) {
+	return Entry{}, s.err
+}
+
+func (s *errStore) Upload(context.Context, string, string, io.Reader) (Entry, error) {
+	return Entry{}, s.err
+}
+
+func (s *errStore) Download(context.Context, string, io.Writer) (int64, error) {
+	return 0, s.err
+}
+
+func (s *errStore) Move(context.Context, []string, string) error { return s.err }
+
+func (s *errStore) Copy(context.Context, []string, string) error { return s.err }
+
+func (s *errStore) Rename(context.Context, string, string) error { return s.err }
+
+func (s *errStore) Delete(context.Context, []string) error { return s.err }
+
+// Files returns the composed file facade. The returned *FileClient implements
+// FileStore, so callers that used Files() as the plain REST store keep working.
+func (c *Client) Files() *FileClient { return c.newFileClient() }
+
+// retryStoreOp runs one store operation under the shared deterministic
+// transient-error policy (429/502/503/504).
+func retryStoreOp(ctx context.Context, fn func() error) error {
+	return DoRetry(ctx, DefaultRetryPolicy(), fn)
+}
+
+// FileEntryToEntry converts a Files-module file row to the canonical model.
+func FileEntryToEntry(f *FileEntry, provider string) Entry {
+	e := Entry{Kind: File, Provider: provider}
+	if f == nil {
+		return e
+	}
+	if f.ID != nil {
+		e.ID = f.ID.String()
+	}
+	e.ParentID = FileFolderID(f)
+	if f.Title != nil {
+		e.Title = *f.Title
+	}
+	if f.ContentLength != nil {
+		e.Size = parseContentLength(*f.ContentLength)
+	}
+	exst := ""
+	if f.FileExst != nil {
+		exst = *f.FileExst
+	}
+	e.MIME = mimeForTitle(e.Title, exst)
+	if f.Updated != nil {
+		e.Modified = *f.Updated
+		e.Updated = f.Updated.Format(time.RFC3339)
+	}
+	return e
+}
+
+// DavFileToEntry converts a WebDAV file row to the canonical model.
+func DavFileToEntry(f DavFile, provider string) Entry {
+	return Entry{
+		ID:       f.ID,
+		Title:    f.Title,
+		Kind:     File,
+		Size:     f.Size,
+		MIME:     mimeForTitle(f.Title, ""),
+		Modified: f.ModTime(),
+		Updated:  f.Updated,
+		Provider: provider,
+	}
+}
+
+// DavFolderToEntry converts a WebDAV folder row to the canonical model.
+func DavFolderToEntry(f DavFolder, provider string) Entry {
+	return Entry{
+		ID:           f.ID,
+		ParentID:     f.ParentID,
+		Title:        f.Title,
+		Kind:         Folder,
+		Modified:     f.ModTime(),
+		Updated:      f.Updated,
+		Provider:     provider,
+		FilesCount:   f.FilesCount,
+		FoldersCount: f.FoldersCount,
+	}
+}
+
+// parseContentLength reads the leading integer of an OnlyOffice contentLength
+// string (the API sometimes appends a unit, e.g. "12345 b").
+func parseContentLength(s string) int64 {
+	fields := strings.Fields(s)
+	if len(fields) == 0 {
+		return 0
+	}
+	n, err := strconv.ParseInt(fields[0], 10, 64)
+	if err != nil {
+		return 0
+	}
+	return n
+}
+
+// mimeForTitle derives a MIME type from an explicit extension or the title.
+func mimeForTitle(title, exst string) string {
+	ext := strings.TrimSpace(exst)
+	if ext == "" {
+		ext = filepath.Ext(title)
+	}
+	if ext == "" {
+		return ""
+	}
+	if !strings.HasPrefix(ext, ".") {
+		ext = "." + ext
+	}
+	return mime.TypeByExtension(strings.ToLower(ext))
+}