docs(api): add universal progress tracking documentation

- get_universal_progress.md - GET /api/progress/:id
- update_universal_progress.md - POST /api/progress/:id
- get_progress_history.md - GET /api/progress/:id/history

Documents device-agnostic (universal) reading progress tracking
that works across all devices (Kobo, KOReader, etc.)

docs/developer/api/book-matching/get_book_matches.md

@@ -0,0 +1,56 @@
+# Get Book Matches
+
+Get potential book matches for a given query.
+
+**Endpoint**: `GET /api/books/match`
+**Auth**: Required
+
+## Query Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|-----------|-------------|
+| q | string | Yes | Search query (title, author, etc.) |
+| limit | integer | No | Maximum number of matches to return (default: 10) |
+
+## Request Headers
+
+| Header | Type | Required | Description |
+|--------|------|-----------|-------------|
+| Authorization | string | Yes | Bearer token |
+
+### Example Request
+
+```http
+GET /api/books/match?q=Foundation+Asimov&limit=5
+Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
+```
+
+## Response (200 OK)
+
+```json
+{
+  "matches": [
+    {
+      "id": "uuid",
+      "title": "Foundation",
+      "authors": ["Isaac Asimov"],
+      "isbn": "978-0553293357",
+      "published_year": 1951,
+      "publisher": "Bantam Books",
+      "cover_url": "https://example.com/cover.jpg"
+    }
+  ],
+  "total": 5
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Missing required query parameter |
+| 401 | Invalid or expired token |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->