docs(files): add unified file client contract (#39)

AGENTS.md

@@ -10,11 +10,12 @@ Canonical Go client for OnlyOffice Workspace (Projects + Calendar + CRM) and the
   - `auth.go` — `Authenticate`, `AuthenticateContext`, `InvalidateToken`, `Auth`, token lifecycle.
   - `http.go` — transport + DRY response decoders (`ResponseArray`/`ResponseObject`/`postFormObject`/`putFormObject`/`deleteObject`).
   - `projects.go`, `tasks.go`, `users.go`, `calendar.go`, `crm.go`, `files.go`, `files_webdav.go`, `files_stem.go`, `retry.go`, `mails.go`, `invoices.go` — typed / untyped domain methods. **`files.go`** — CRM opportunity upload plus **project/task Documents** (`UpdateFile`, `UploadToFolderReplacing`). **`files_webdav.go`** — Documents module by id (`ListDavFolder`, `MoveDavItems`/`CopyDavItems` with per-operation error surfacing, `ListFileOps`). **`retry.go`** — `DoRetry`: deterministic linear backoff (no jitter) on 429/502/503/504; every bulk tool routes API calls through it. **`mails.go`** — OnlyOffice Workspace Mail. **`invoices.go`** — CRM invoices, PDF regen/cleanup, status. Association rules: [`docs/crm-associations.md`](docs/crm-associations.md).
+  - **Unified file client (epic #34) — `file_core.go`, `file_rest.go`, `file_dav.go`, `file_pg.go`, `file_es.go`, `file_es_text.go`, `file_text_index.go`, `file_facade.go`.** `file_core.go` — model (`Entry`, `Kind`) + `FileStore`/`Searcher`; `file_rest.go`/`file_dav.go` — REST/WebDAV adapters; `file_pg.go` — **read-only** SQL store (PostgreSQL/MySQL, `ErrReadOnly` on writes); `file_es.go` — OnlyOffice Elasticsearch searcher; `file_es_text.go`/`file_text_index.go` — own PDF/scan index (`oo_docs_text`, PDF attachments via pdfdetach); `file_facade.go` — `FileClient` with read/write/search order and transient fallback. Use `c.Files()` (facade) or `c.FileStore("rest"|"dav")`; contract and how to add a backend: [`docs/unified-file-client.md`](docs/unified-file-client.md).
   - Pure stdlib + `google/go-querystring`; no UI, no dotenv.
 - **CLI — `cmd/oo/` as `package main`.** Cobra wrapper that loads `.env` via `godotenv` at startup. **Subject-based command tree** mirroring [`tea`](https://gitea.com/gitea/tea):
   - `main.go` — entry point (docstring lists the command tree).
   - `common.go` — `rootCmd`, `newOO`, `printTable`/`printObject`, `--output table|json` flag.
-  - `calendar.go`, `projects.go`, `projects_files.go`, `tasks.go`, `tasks_files.go`, `users.go`, `contacts.go`, `opportunities.go`, `cases.go`, `crm.go`, `crm_tasks.go`, `catalog.go`, `docs.go`, `dav.go`, `mails.go`, `invoices.go` — one file per subject (or per subject facet), each registers in `init()`. `dav.go` exposes the Documents module by id (`oo dav ls|move|copy|mkdir|rename-file|rename-folder|download|fileops`).
+  - `calendar.go`, `projects.go`, `projects_files.go`, `tasks.go`, `tasks_files.go`, `users.go`, `contacts.go`, `opportunities.go`, `cases.go`, `crm.go`, `crm_tasks.go`, `catalog.go`, `docs.go`, `dav.go`, `search.go`, `index.go`, `mails.go`, `invoices.go` — one file per subject (or per subject facet), each registers in `init()`. `dav.go` exposes the Documents module by id (`oo dav ls|move|copy|mkdir|rename-file|rename-folder|download|fileops`); `search.go` runs `oo search QUERY` (name/content, `--backend oo|own`); `index.go` fills the own full-text index (`oo index folder|files`, see [`docs/unified-file-client.md`](docs/unified-file-client.md)).
   - CLI-only deps (`spf13/cobra`, `joho/godotenv`) stay out of the library.
 - **TUI — `cmd/office/` as `package main`.** Bubble Tea three-pane browser (module tree, selectable list, markdown preview). Reuses `cmd/internal/bootstrap` for env/auth and the root `onlyoffice` library for all API calls. UI logic in `cmd/office/ui/`; preview/formatting in `cmd/office/preview/`; list loaders in `cmd/office/fetch/`.
   - **List table (`DataTable`)** — `cmd/office/ui/table*.go`. Column layout policies live in `cmd/office/model/table_layout.go` (`TableFlexLayoutFor`); cell rendering uses the bubbles/table inline pattern in `table_render.go` (`renderTableCell`, `padANSIWidth`). See `.cursor/skills/office-tui-table/SKILL.md` before changing center-pane tables.