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.

internal/health/database.go

@@ -1,3 +1,4 @@
+// Package health provides health check implementations for various components.
 package health
 
 import (
@@ -23,4 +24,3 @@ func NewDatabaseChecker(client *database.Client) health.HealthChecker {
 func (d *DatabaseChecker) Check(ctx context.Context) error {
 	return d.client.Ping(ctx)
 }
-