docs(highlights,notes,opds,progress,analytics): Beam batch 9 — 13 endpoints

Highlights + notes CRUD (media-item scoped, jwt), progress delete,
reading-stats analytics, and the OPDS trio frontmatter'd. OPDS docs are
the first XML entries: example-response intentionally omitted (Atom
responses), gate contract honored via nil-Response registry pins.

Gate fix: group .Use() middleware now parsed (opds.Use(DeviceAuth...
Authenticate) previously resolved to auth 'none'). Registry: 13 entries.
Drift fixed by gate: reading-stats key names (total_reading_time_minutes,
most_active_day_of_week, daily_reading_minutes — draft invented
reading_time_hours/books_completed); notes/highlights list endpoints
return BARE arrays (no {notes:[]}/{highlights:[]} wrapper); create-note
request has no percentage_location/epubcfi_location. New
/tmp/merge_arrays.py handles array-example merges.

make test 9/9.

docs/developer/api/progress/delete_media_progress.md

@@ -1,3 +1,11 @@
+---
+method: DELETE
+path: /api/media-items/:id/progress
+auth: jwt
+area: media-items
+---
+<!-- source: internal/handlers/media.go:1350 MediaHandler.DeleteMediaReadingProgress -->
+
 # Delete Media Item Progress
 
 Delete the stored reading progress for a media item.
@@ -20,7 +28,7 @@ Authorization: Bearer eyJhbGciOiJIUzI1NiIs...
 
 ## Response (200 OK)
 
-```json
+```json example-response
 {
   "message": "reading progress deleted"
 }