chore(git): ignore *.db* per workflow policy, untrack db/custom.db

The SQLite database is runtime state (presets, settings, sessions)
written constantly by the live app -- it is regenerated per machine via
prisma db push and seeded from embedded presets on first boot, so it
does not belong in version control. The file remains on disk untouched.

Also adds *.sqlite / *.sqlite3 alongside the requested *.db* pattern.

.gitignore

@@ -35,6 +35,11 @@ yarn-error.log*
 .env*
 !.env.example
 
+# databases -- runtime state, regenerated per machine (prisma db push)
+*.db*
+*.sqlite
+*.sqlite3
+
 # vercel
 .vercel