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_this_week.md

@@ -0,0 +1,48 @@
+---
+method: GET
+path: /api/stats/this-week
+auth: jwt
+area: stats
+---
+<!-- source: internal/handlers/stats.go:56 StatsHandler.ThisWeek -> services/statistics_service.go:451 WeekSummaryStats -->
+
+# Get This Week's Stats
+
+Compact week-vs-previous-week comparison powering the dashboard widget.
+Week boundaries are the requesting user's calendar week (timezone-aware).
+
+## Query Parameters
+
+| Parameter  | Type          | Required | Description                             |
+| ---------- | ------------- | -------- | --------------------------------------- |
+| library_id | string (UUID) | No       | Scope totals to one library             |
+
+## Example Request
+
+```http
+GET /api/stats/this-week
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Example response
+
+```json example-response
+{
+  "week_minutes": 315,
+  "week_pages": 122,
+  "week_sessions": 21,
+  "week_books": 3,
+  "prev_week_minutes": 402,
+  "prev_week_pages": 160,
+  "prev_week_sessions": 25,
+  "active_today": true,
+  "current_streak": 5
+}
+```
+
+## Errors
+
+| Status | Body                 | When                   |
+| ------ | -------------------- | ---------------------- |
+| 400    | `invalid library id` | malformed library_id   |
+| 401    | `invalid user`       | no user in JWT context |