fix(scraper): add EnsureMigrations to patch progress.user_id on startup

On every scraper startup, EnsureMigrations fetches each collection schema
and PATCHes in any missing fields. This repairs the progress collection on
cloud deploys where pb-init ran before user_id was added to the schema.
No-ops when the field already exists.

scraper/internal/storage/pocketbase.go

@@ -389,6 +389,82 @@ func (s *PocketBaseStore) EnsureCollections(ctx context.Context) error {
 	return nil
 }
 
+// ─── Schema migrations ────────────────────────────────────────────────────────
+
+// migration describes a single field to guarantee exists in a collection.
+type migration struct {
+	collection string
+	fieldName  string
+	fieldType  string
+}
+
+// migrations is the ordered list of schema changes applied on every startup.
+var migrations = []migration{
+	// user_id was added to progress after initial deploy.
+	{"progress", "user_id", "text"},
+}
+
+// EnsureMigrations idempotently adds any fields that are missing from existing
+// collections. It fetches the current schema, checks for each field by name,
+// and PATCHes the collection only when something is absent.
+// Safe to call on every startup — no-ops when schema is already up to date.
+func (s *PocketBaseStore) EnsureMigrations(ctx context.Context) error {
+	for _, m := range migrations {
+		if err := s.ensureField(ctx, m); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (s *PocketBaseStore) ensureField(ctx context.Context, m migration) error {
+	// Fetch current collection schema.
+	resp, err := s.pb.do(ctx, http.MethodGet, "/api/collections/"+m.collection, nil)
+	if err != nil {
+		return fmt.Errorf("pocketbase: ensureField %s.%s: fetch schema: %w", m.collection, m.fieldName, err)
+	}
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(resp.Body)
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("pocketbase: ensureField %s.%s: fetch schema status %d: %s", m.collection, m.fieldName, resp.StatusCode, body)
+	}
+
+	var schema struct {
+		ID     string                   `json:"id"`
+		Fields []map[string]interface{} `json:"fields"`
+	}
+	if err := json.Unmarshal(body, &schema); err != nil {
+		return fmt.Errorf("pocketbase: ensureField %s.%s: decode schema: %w", m.collection, m.fieldName, err)
+	}
+
+	// Check if field already exists.
+	for _, f := range schema.Fields {
+		if name, _ := f["name"].(string); name == m.fieldName {
+			s.log.Debug("pocketbase: field already exists, skipping migration",
+				"collection", m.collection, "field", m.fieldName)
+			return nil
+		}
+	}
+
+	// Append the new field and PATCH the collection.
+	newFields := append(schema.Fields, map[string]interface{}{
+		"name": m.fieldName,
+		"type": m.fieldType,
+	})
+	patch := map[string]interface{}{"fields": newFields}
+	patchResp, err := s.pb.do(ctx, http.MethodPatch, "/api/collections/"+schema.ID, patch)
+	if err != nil {
+		return fmt.Errorf("pocketbase: ensureField %s.%s: patch: %w", m.collection, m.fieldName, err)
+	}
+	defer patchResp.Body.Close()
+	patchBody, _ := io.ReadAll(patchResp.Body)
+	if patchResp.StatusCode != http.StatusOK {
+		return fmt.Errorf("pocketbase: ensureField %s.%s: patch status %d: %s", m.collection, m.fieldName, patchResp.StatusCode, patchBody)
+	}
+	s.log.Info("pocketbase: schema migration applied", "collection", m.collection, "field", m.fieldName, "type", m.fieldType)
+	return nil
+}
+
 // ─── Book metadata ────────────────────────────────────────────────────────────
 
 func (s *PocketBaseStore) UpsertBook(ctx context.Context, slug, title, author, cover, status, summary, sourceURL string, genres []string, totalChapters, ranking int) error {