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)
 }
-

internal/health/registry.go

@@ -60,7 +60,7 @@ func (r *Registry) Check(ctx context.Context) health.HealthStatus {
 }
 
 // LivenessCheck performs a basic liveness check (no dependencies).
-func (r *Registry) LivenessCheck(ctx context.Context) health.HealthStatus {
+func (r *Registry) LivenessCheck(_ context.Context) health.HealthStatus {
 	// Liveness is always healthy if the service is running
 	return health.HealthStatus{
 		Status: health.StatusHealthy,
@@ -71,4 +71,3 @@ func (r *Registry) LivenessCheck(ctx context.Context) health.HealthStatus {
 func (r *Registry) ReadinessCheck(ctx context.Context) health.HealthStatus {
 	return r.Check(ctx)
 }
-