feat: Implement Session Token System with /api/v1 base path

- Add migration 000004 for sessions table and performance indexes
- Create session.sql queries for CRUD operations
- Generate session repository code with sqlc
- Create token auth middleware for Echo framework
- Create token handler with create/delete/cleanup endpoints
- Add /api/v1 router with token authentication infrastructure
- Update dbHelper.go to use Up() instead of Migrate(2)
- Update server.go to initialize token handler
- Existing endpoints remain functional (to be deprecated)

New endpoints:
- POST /api/v1/token - Create new session token
- DELETE /api/v1/token - Invalidate token
- POST /api/v1/token/cleanup - Remove expired sessions

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/db/migrations/000004_create_sessions_table_and_indexes.down.sql

@@ -0,0 +1,24 @@
+-- Drop indexes for sessions table
+DROP INDEX IF EXISTS idx_sessions_expires;
+DROP INDEX IF EXISTS idx_sessions_token;
+DROP INDEX IF EXISTS idx_sessions_ip;
+DROP INDEX IF EXISTS idx_sessions_created;
+
+-- Drop sessions table
+DROP TABLE IF EXISTS sessions;
+
+-- Drop performance indexes for song_list
+DROP INDEX IF EXISTS idx_song_list_match_date;
+DROP INDEX IF EXISTS idx_song_list_match_id;
+
+-- Drop performance indexes for song
+DROP INDEX IF EXISTS idx_song_hash;
+DROP INDEX IF EXISTS idx_song_path;
+DROP INDEX IF EXISTS idx_song_game_id;
+DROP INDEX IF EXISTS idx_song_game_id_song_name;
+
+-- Drop performance indexes for game
+DROP INDEX IF EXISTS idx_game_deleted;
+DROP INDEX IF EXISTS idx_game_hash;
+DROP INDEX IF EXISTS idx_game_path;
+DROP INDEX IF EXISTS idx_game_name;