refactor: chats method shebangs; drop chats index (D14). (#11)

Parsers and commands live in internal/chats. bin/chats/{sync,import,facts,apply}.go
are tagged shebang mains. Brain ingest is not a chats command.

internal/chats/source.go

@@ -0,0 +1,52 @@
+package chats
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"time"
+)
+
+type Source interface {
+	Name() string
+	Sync(ctx context.Context, outDir string, limit int) error
+}
+
+type Message struct {
+	ID        string  `json:"id"`
+	Timestamp string  `json:"ts"`
+	From      string  `json:"from"`
+	Text      string  `json:"text"`
+	Media     *string `json:"media,omitempty"`
+	Platform  string  `json:"platform"`
+}
+
+type ChatInfo struct {
+	ID           string   `json:"id"`
+	Platform     string   `json:"platform"`
+	Name         string   `json:"name"`
+	Participants []string `json:"participants"`
+	Type         string   `json:"type"`
+	MessageCount int      `json:"messageCount"`
+	LastTS       string   `json:"lastTs,omitempty"`
+}
+
+func envVar(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}
+
+func parseSince(s string) (time.Time, error) {
+	for _, layout := range []string{
+		time.RFC3339,
+		"2006-01-02T15:04:05",
+		"2006-01-02",
+	} {
+		if t, err := time.Parse(layout, s); err == nil {
+			return t, nil
+		}
+	}
+	return time.Time{}, fmt.Errorf("cannot parse --since %q; use YYYY-MM-DD or RFC3339", s)
+}