refactor(api): rename ScanEbooks to ScanLibrary for clarity

- Rename ScanEbooks method to ScanLibrary to reflect generic media scanning

- Rename ScanEbooksRequest to ScanLibraryRequest

- Update route handlers in scanner.go and library.go

- Rename scan_ebooks.md to scan_library.md

- No breaking changes: API endpoint remains POST /api/scanner/scan

docs/developer/api/scanner/scan_library.md

@@ -0,0 +1,59 @@
+# Scan Library
+
+Initiate a one-time scan of a library for ebooks, manga, or comics.
+
+**Endpoint**: `POST /api/scanner/scan`
+**Auth**: Required (Admin only)
+**Content-Type**: `application/json`
+
+## Request Body
+
+| Field | Type | Required | Description |
+|--------|------|-----------|-------------|
+| library_id | string (UUID) | Yes | Library UUID to scan (supports ebooks, manga, and comics) |
+| recursive | boolean | No | Scan subdirectories recursively (default: true) |
+| force | boolean | No | Force rescan of existing files (default: false) |
+
+## Supported Formats
+
+The scanner automatically detects and processes files based on the library type:
+
+**Ebooks:** .epub, .pdf, .mobi, .azw, .azw3, .txt, .rtf, .doc, .docx, .lit, .fb2, .pdb
+
+**Comics:** .cbz, .cbr, .cb7, .cbt, .pdf
+
+**Manga:** .cbz, .cbr, .png, .jpg, .jpeg, .gif, .bmp, .webp
+
+### Example Request
+
+```json
+{
+  "library_id": "550e8400-e29b-41d4-a716-446655440000",
+  "recursive": true,
+  "force": false
+}
+```
+
+## Response (202 Accepted)
+
+```json
+{
+  "message": "Scan initiated successfully",
+  "job_id": "uuid",
+  "library_id": "uuid",
+  "status": "pending"
+}
+```
+
+## Error Responses
+
+| Code | Description |
+|------|-------------|
+| 400 | Invalid request data |
+| 401 | Invalid or expired token |
+| 403 | User does not have admin privileges |
+| 404 | Library not found |
+
+## Try It Out
+
+<!-- API Explorer will be inserted here in Phase 3 -->