fix: resolve all linting and formatting issues

- Fix error return value checks (errcheck)
- Fix unused parameters by using underscore prefix
- Add missing package comments to all packages
- Fix context key type issue in middleware (use typed contextKey)
- Replace deprecated trace.NewNoopTracerProvider with noop.NewTracerProvider
- Fix embedded field selector in database client
- Remove trailing whitespace
- Remove revive linter (as requested) to avoid stuttering warnings for public API interfaces

All linting and formatting checks now pass.

pkg/health/health.go

@@ -1,3 +1,4 @@
+// Package health provides interfaces and types for health checking.
 package health
 
 import "context"
@@ -31,4 +32,3 @@ type HealthStatus struct {
 	Status     Status            `json:"status"`
 	Components []ComponentStatus `json:"components,omitempty"`
 }
-