add dev-only profiling with pprof, runtime/trace, and operation timing

Wire up Go's standard profiling toolkit so it's automatically available
in dev builds and completely absent from production. The profiling
package uses build tags (dev/!dev) to eliminate all pprof, trace, and
timing code from release binaries with zero new dependencies.

- backend/profiling: pprof HTTP server on :6060, /debug/trace endpoint,
  block/mutex profiling, and TimeOp helper for structured operation timing
- scripts/profile.sh: interactive menu-driven script that auto-selects
  free ports (8080-8089) so multiple profiles can be open simultaneously
- Instrumented key operations: app init, database init, player load/restore,
  queue set/restore
- Makefile targets: profile, profile-cpu, profile-heap, profile-trace
- .gitignore: exclude trace-*.out and *.pprof artifacts

backend/app.go

@@ -19,6 +19,7 @@ import (
 	"yellowjacket/backend/library"
 	"yellowjacket/backend/player"
 	"yellowjacket/backend/playlist"
+	"yellowjacket/backend/profiling"
 	"yellowjacket/backend/queue"
 )
 
@@ -43,6 +44,8 @@ func NewYellowJacketApp(
 	logger *slog.Logger,
 	assetHandler *assets.Handler,
 ) (*YellowJacketApp, error) {
+	defer profiling.TimeOp(logger, "app.NewYellowJacketApp")()
+
 	// initialize anything that does not need access to the wails runtime here
 	yjApp := &YellowJacketApp{
 		logger:       logger,
@@ -118,6 +121,8 @@ var startupErr error
 
 // OnStartup initializes components that require the Wails runtime context.
 func (yj *YellowJacketApp) OnStartup(ctx context.Context) {
+	defer profiling.TimeOp(yj.logger, "app.OnStartup")()
+
 	// initialize anything that needs to use the wails runtime AFTER its been initialized
 	// you CANNOT use the wails runtime during this function
 	yj.appContext = ctx