fix: resolve all lint errors and make linting a required CI check (#62)

- Fix 10 err113 violations: extract dynamic errors to package-level sentinels
- Fix 12 errcheck violations: handle unchecked error returns in player,
  metadata, and config packages
- Fix 4 revive stutter warnings: rename player.PlayerState to player.State,
  player.PlayerVolume to player.Volume, queue.QueueTrack to queue.Track,
  queue.QueueState to queue.State
- Fix 2 staticcheck SA4001: simplify *&x to x in assets handler
- Fix 5 unused constants: remove dead AudioFileType iota block in models
- Fix gci/gofumpt/wsl formatting issues across multiple files
- Add gofumpt module-path setting to .golangci.yml for correct import grouping
- Fix player test: gate integration test behind YELLOWJACKET_INTEGRATION env var
  instead of only skipping in CI, and replace t.Errorf+t.Failed with t.Fatalf
- Remove continue-on-error from golangci-lint CI step so linting is now required

backend/assets/handler.go

@@ -39,7 +39,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.logger.Debug(
 			"custom handler for request not found, using wails asset handler",
 			"path",
-			*&r.URL.Path,
+			r.URL.Path,
 		)
 		h.wailsAssetHandler.ServeHTTP(w, r)
 
@@ -49,7 +49,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	h.logger.Debug(
 		"using custom handler for request",
 		"path",
-		*&r.URL.Path,
+		r.URL.Path,
 	)
 	h.serveMux.ServeHTTP(w, r)
 }