feat(docs): drift gate — docs frontmatter validated against real routes

Every API doc that declares frontmatter (method/path/auth/area) is now
checked by a unit test against three sources of truth:

1. Route registration: internal/router/*.go is parsed the way echo resolves
   it (group prefixes concatenate; scanner.go's parameterized groups seeded).
   Doc paths that no longer exist fail. (This is the check that would have
   caught the /api/api/admin/hash-conflicts split.)
2. Auth: frontmatter auth label must match the middleware chain
   (none|jwt|jwt+admin|device-token|optional-jwt).
3. Shapes: internal/docs/schema.go registry — example-request decoded with
   unknown fields DISALLOWED (typo guard), required-by-validate fields must
   appear (staleness guard), example-response top-level key set compared
   both directions against the marshaled handler type (or a RawMessage pin
   for hand-built map responses).

Five collections docs are the pilots with real handler shapes; notable
corrections they pin: update returns 201 (not 200), list excludes smart
collections unless include_auto=true, rule priority is 1-10 higher-wins
(docs claimed 1=highest), created_at is Go time.String() not RFC3339,
hide_finished/show_up_next toggles documented. CollectionResponse hoisted
out of GetCollections/GetBookCollections as CollectionSummary /
BookCollectionSummary so the registry can pin real types.

The gate fails on missing registry entries by design — that is the
maintenance contract. Known pre-existing (not this commit): vet copy-lock
warnings in media.go.

docs/developer/api/collections/list_collections.md

@@ -1,57 +1,77 @@
+---
+method: GET
+path: /api/collections
+auth: jwt
+area: collections
+---
+<!-- source: internal/handlers/collections.go:153 CollectionHandler.GetCollections -->
+
 # List Collections
 
-Get all collections for the authenticated user.
+Lists the signed-in user's collections with live book counts. Smart
+(rule-driven) collections are **excluded by default** so legacy readers never
+see stale membership — pass `include_auto=true` to include them.
 
-**Endpoint**: `GET /api/collections`
-**Auth**: Required
-**Content-Type**: `application/json`
+## Example request
 
-## Query Parameters
+```text
+GET /api/collections?include_auto=true&sort_by=name
+```
 
-| Parameter | Type    | Required | Description                                   |
-| --------- | ------- | -------- | --------------------------------------------- |
-| limit     | integer | No       | Number of collections to return (default: 50) |
-| offset    | integer | No       | Number of collections to skip (default: 0)    |
+## Example response
 
-## Response (200 OK)
-
-```json
+```json example-response
 {
   "collections": [
     {
       "id": "550e8400-e29b-41d4-a716-446655440000",
-      "name": "Science Fiction",
-      "description": "My sci-fi collection",
-      "color": "#FF5733",
-      "icon": "🚀",
-      "auto_assign_rules": [
-        {
-          "field": "genre",
-          "operator": "equals",
-          "value": "Science Fiction",
-          "priority": 1,
-          "enabled": true
-        }
-      ],
-      "view_settings": {
-        "kobo": {
-          "view_mode": "grid",
-          "sort_order": "name",
-          "items_per_page": 24
-        }
-      },
-      "created_at": "2026-02-01T10:00:00Z"
+      "name": "To Read",
+      "description": "Books I want to read soon",
+      "color": "#00FF00",
+      "icon": "📖",
+      "auto_assign_rules": null,
+      "created_at": "2026-10-24 13:57:01.81234 +0000 UTC",
+      "book_count": 12,
+      "is_smart": false
     }
   ],
   "total": 1
 }
 ```
 
-## Error Responses
+`created_at` uses Go's `time.String()` format, not RFC3339.
 
-| Code | Description             |
-| ---- | ----------------------- |
-| 401  | Authentication required |
-| 500  | Internal server error   |
+## Query parameters
 
-## Try It Out
+| Param | Type | Default | Notes |
+| ----- | ---- | ------- | ----- |
+| include_auto | boolean | `false` | include smart collections |
+| sort_by | string | — | `name` sorts alphabetically; otherwise service order |
+| library_id | uuid | — | scopes book counts to one library (smart collections only) |
+
+## Response fields
+
+| Field | Type | Notes |
+| ----- | ---- | ----- |
+| collections | array | `CollectionSummary` objects, see below |
+| total | number | length of `collections` |
+
+### Collection item
+
+| Field | Type | Notes |
+| ----- | ---- | ----- |
+| id | string (uuid) | |
+| name | string | |
+| description | string | |
+| color | string | |
+| icon | string | |
+| auto_assign_rules | array \| null | raw rules JSON; non-null implies smart |
+| created_at | string | Go `time.String()` format |
+| book_count | number | live count; respects `library_id` for smart collections |
+| is_smart | boolean | |
+
+## Errors
+
+| Status | Body | When |
+| ------ | ---- | ---- |
+| 500 | `{"error": "..."}` | unexpected server error |