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/analytics/get_analytics.md

@@ -1,3 +1,11 @@
+---
+method: GET
+path: /api/analytics/reading-stats
+auth: jwt
+area: analytics
+---
+<!-- source: internal/handlers/analytics.go:72 AnalyticsHandler.GetReadingStats -->
+
 # Get Reading Statistics
 
 Retrieve reading statistics for a date range.
@@ -27,13 +35,16 @@ Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
 
 ## Response (200 OK)
 
-```json
+```json example-response
 {
-  "pages_read": 1250,
-  "books_completed": 5,
-  "reading_time_hours": 42.5,
-  "sessions_count": 28,
-  "average_session_minutes": 91
+  "average_session_time_minutes": null,
+  "completion_rate": null,
+  "daily_reading_minutes": null,
+  "longest_session_minutes": null,
+  "most_active_day_of_week": null,
+  "total_books_read": null,
+  "total_pages_read": null,
+  "total_reading_time_minutes": null
 }
 ```