feat: add local files provider with indexing and rescan functionality

- Implemented LocalFilesProvider to manage local video files.
- Added LocalIndex for in-memory and SQLite-backed indexing of video files.
- Introduced scanning functionality to detect video files and extract metadata.
- Added API endpoints for listing collections, genres, and series based on provider capabilities.
- Enhanced existing routes to check for provider capabilities before processing requests.
- Updated frontend to utilize provider capabilities for conditional rendering of UI elements.
- Implemented rescan functionality to refresh the local files index.
- Added database migration for local files index schema.

k-tv-backend/migrations_sqlite/20260314000000_add_local_files_index.sql

@@ -0,0 +1,10 @@
+CREATE TABLE IF NOT EXISTS local_files_index (
+    id          TEXT    PRIMARY KEY,
+    rel_path    TEXT    NOT NULL UNIQUE,
+    title       TEXT    NOT NULL,
+    duration_secs INTEGER NOT NULL DEFAULT 0,
+    year        INTEGER,
+    tags        TEXT    NOT NULL DEFAULT '[]',
+    top_dir     TEXT    NOT NULL DEFAULT '',
+    scanned_at  TEXT    NOT NULL
+);