docs(stats): Claude-side pinning — all 4 stats endpoints + UNVERIFIED sweep to zero

Stats docs written handler/service-first (summary/this-week/book-stats
new; library-usage frontmatter'd — its body was already accurate).
Registry: 4 entries on services.UserSummaryStats/WeekSummaryStats/
LibraryUsageStats/BookStats. Family-lens note: library-usage 403s an
explicit library_id outside the visible set (431fec0 rule).

UNVERIFIED sweep (7 -> 0), each resolved against the handler:
- device-usage takes NO date params; popular-books takes only ?limit
  (the 'standard analytics date-range params' claim was wrong)
- link_book media_item_id: no validate tag but service-always-written
- push_stats book-ref field set documented (uuid/sha256/title/authors)
- filter_count: confirmed ParseMediaSearchParams machinery + 400 on bad
  filter + 403 visibility
- facets values element shape pinned: {value, display?, count}
- get_config: dynamic key set IS the contract (reworded, no marker)

make test 9/9.

docs/developer/api/stats/get_book_stats.md

@@ -0,0 +1,60 @@
+---
+method: GET
+path: /api/stats/books/:id
+auth: jwt
+area: stats
+---
+<!-- source: internal/handlers/stats.go:118 StatsHandler.BookStats -> services/statistics_service.go:697 BookStats -->
+
+# Get Book Stats
+
+Per-book reading card on the book detail page: lifetime totals plus recent
+sessions (newest first, capped). Scoped to the requesting user's own
+reading history.
+
+## Example Request
+
+```http
+GET /api/stats/books/550e8400-e29b-41d4-a716-446655440000
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Example response
+
+```json example-response
+{
+  "media_item_id": "550e8400-e29b-41d4-a716-446655440000",
+  "total_minutes": 610,
+  "total_seconds": 36612,
+  "total_pages": 0,
+  "session_count": 41,
+  "max_progress": 0.62,
+  "finished": false,
+  "first_session": "2026-09-30T18:02:11Z",
+  "last_session": "2026-10-23T21:44:05Z",
+  "recent_sessions": [
+    {
+      "started_at": "2026-10-23T21:44:05Z",
+      "ended_at": "2026-10-23T22:19:40Z",
+      "minutes": 35,
+      "pages": 0,
+      "device_id": "660e8400-e29b-41d4-a716-446655440001"
+    }
+  ]
+}
+```
+
+## Response fields
+
+| Field         | Type    | Notes                                                            |
+| ------------- | ------- | ---------------------------------------------------------------- |
+| total_seconds | int     | exact wall-clock (audio "Time listened"; minutes lose remainder) |
+| max_progress  | float   | highest progress fraction ever reached (0-1)                     |
+| recent_sessions | array | newest first, server-capped                                      |
+
+## Errors
+
+| Status | Body                     | When                    |
+| ------ | ------------------------ | ----------------------- |
+| 400    | `invalid media item id`  | malformed id            |
+| 401    | `invalid user`           | no user in JWT context  |