docs: remove Phase X placeholders from API documentation

Clean up API documentation files by removing Phase X references:

Remove 'API Explorer will be inserted here in Phase X' placeholders from:
- 70+ API endpoint documentation files
- Authentication endpoints (login, logout, register, refresh)
- User endpoints (profile, settings, password)
- Device endpoints (registration, sync, shelves)
- Library endpoints (CRUD, folders, visibility)
- Media endpoints (items, progress, highlights, notes)
- Admin endpoints (users, analytics)
- Sync endpoints (Kobo, KOReader)
- OPDS endpoints
- Scanner endpoints
- Queue endpoints

These placeholders were from planning documents and have no meaning
to API consumers. The documentation is now clean and ready for use.

docs/developer/api/kobo/analytics_gettests.md

@@ -40,7 +40,3 @@ This endpoint requires device authentication (not user JWT). This is a Kobo comp
 ## Notes
 
 This is a Kobo compatibility endpoint used by Kobo devices for analytics purposes. The exact request/response format follows Kobo's proprietary protocol.
-
-## Try It Out
-
-<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/kobo/bookmark_sync.md

@@ -57,7 +57,3 @@ This endpoint requires device authentication (not user JWT). Kobo devices authen
 | 401 | Device authentication failed |
 | 400 | Invalid request data |
 | 404 | Device or book not found |
-
-## Try It Out
-
-<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/kobo/initialization.md

@@ -47,7 +47,3 @@ X-Device-Key: device-auth-key
 ## Notes
 
 This endpoint is called by Kobo devices during initial setup and connection. It returns configuration data required for proper Kobo integration.
-
-## Try It Out
-
-<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/kobo/markup_sync.md

@@ -65,7 +65,3 @@ This endpoint requires device authentication (not user JWT). Kobo devices authen
 | 401 | Device authentication failed |
 | 400 | Invalid request data |
 | 404 | Device or book not found |
-
-## Try It Out
-
-<!-- API Explorer will be inserted here in Phase 3 -->

docs/developer/api/kobo/sync_from_server.md

@@ -61,7 +61,3 @@ This endpoint requires device authentication (not user JWT). Kobo devices authen
 ## Notes
 
 This endpoint pushes library content from the server to the Kobo device. It's called during sync operations to update the device's library catalog.
-
-## Try It Out
-
-<!-- API Explorer will be inserted here in Phase 3 -->