docs(media-items): Work Order 3 batch 3b — management endpoints (8)

New frontmatter'd docs:
- download (ServeFile — raw bytes, family-lens enforced; corrects the old
  download doc's claim that no download route is registered: ServeFile IS
  routed, DownloadBook is the dead code)
- set_audio_speed (speed range 0.25-4.0, NaN/Inf rejected)
- rescan (abridged example over the full 70+-column row; write-after-success
  guarantee noted)
- purge-archived (destructive, admin), unarchive (204), merge (SHA-256
  precondition, per-user collisions keep active copy)
- facets (two modes: facet+values, field autocomplete counts)
- filter_count (family lens)

Registry: RawMessage pins for map/abridged responses; Schema{} for non-JSON
body routes (download = raw bytes; unarchive = 204). Audit now:
missing docs down to ~55 (from 112), 0 orphans.

internal/docs/schema.go

@@ -207,4 +207,35 @@ var Schemas = map[string]Schema{
 		Request:  nil, // kind via required ?annotation_type=
 		Response: json.RawMessage(`{"purged": false}`),
 	},
+
+	// --- media-items batch 3b: management ---
+	"GET /api/media-items/:id/download": {
+		// Serves raw file bytes, not JSON — no examples by design.
+	},
+	"PUT /api/media-items/:id/audio-speed": {
+		Request:  json.RawMessage(`{"speed": 0}`),
+		Response: json.RawMessage(`{"playback_speed": 0}`),
+	},
+	"POST /api/media-items/:id/rescan": {
+		// Returns the FULL media_items row (70+ columns); pin is an abridged
+		// key subset — the doc example declares the same subset and says so.
+		Response: json.RawMessage(`{
+			"id": "", "library_id": "", "title": "", "author": "",
+			"file_path": "", "mime_type": "", "scan_status": "", "updated_at": ""
+		}`),
+	},
+	"POST /api/media-items/purge-archived": {
+		Response: json.RawMessage(`{"purged": 0}`),
+	},
+	"POST /api/media-items/:id/unarchive": {},
+	"POST /api/media-items/:id/merge": {
+		Request:  json.RawMessage(`{"target_id": ""}`),
+		Response: json.RawMessage(`{"message": ""}`),
+	},
+	"GET /api/media-items/facets": {
+		Response: json.RawMessage(`{"facet": "", "values": [{}]}`),
+	},
+	"GET /api/media-items/filter-count": {
+		Response: json.RawMessage(`{"count": 0}`),
+	},
 }