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/database/database.go

@@ -11,6 +11,7 @@ import (
 	"path"
 
 	_ "modernc.org/sqlite" // Register sqlite driver.
+
 	"yellowjacket/backend/database/sql/sqlcgen"
 	"yellowjacket/backend/system"
 )
@@ -61,6 +62,7 @@ func NewDB(logger *slog.Logger) (*DB, error) {
 	for _, dirEntry := range dirEntries {
 		if !dirEntry.IsDir() {
 			filePath := path.Join("sql/schemas", dirEntry.Name())
+
 			sqlContent, err := fs.ReadFile(schemas, filePath)
 			if err != nil {
 				return nil, fmt.Errorf("could not read file %s: %w", filePath, err)