fix: resolve all golangci-lint issues

- Add package comments to all packages (pkg/config, pkg/logger, internal/*, cmd/platform)

- Fix context key warnings by using custom ContextKey type
  - Export ContextKey type to avoid unexported-return warnings
  - Update all context value operations to use ContextKey instead of string
  - Update RequestIDKey() and UserIDKey() to return ContextKey

- Fix error checking issues (errcheck)
  - Properly handle os.Chdir errors in defer statements
  - Properly handle os.Setenv/os.Unsetenv errors in tests

- Fix security warnings (gosec)
  - Change directory permissions from 0755 to 0750 in tests
  - Change file permissions from 0644 to 0600 in tests

- Fix unused parameter warnings (revive)
  - Replace unused parameters with _ in:
    * RegisterLifecycleHooks lifecycle functions
    * Mock logger implementations
    * noOpLogger methods

- Fix type assertion issues (staticcheck)
  - Remove unnecessary type assertions in tests
  - Use simpler compile-time checks

- Fix exported type stuttering warning
  - Add nolint directive for ConfigProvider (standard interface pattern)

- Update golangci-lint configuration
  - Add version: 2 field (required for newer versions)
  - Remove unsupported linters (typecheck, gosimple)
  - Move formatters (gofmt, goimports) to separate formatters section
  - Simplify linter list to only well-supported linters

All linting issues resolved (0 issues reported by golangci-lint).
All tests pass and code compiles successfully.

internal/di/container.go

@@ -1,3 +1,4 @@
+// Package di provides dependency injection container and providers using uber-go/fx.
 package di
 
 import (

internal/di/providers.go

@@ -67,13 +67,13 @@ func CoreModule() fx.Option {
 // RegisterLifecycleHooks registers lifecycle hooks for logging.
 func RegisterLifecycleHooks(lc fx.Lifecycle, l logger.Logger) {
 	lc.Append(fx.Hook{
-		OnStart: func(ctx context.Context) error {
+		OnStart: func(_ context.Context) error {
 			l.Info("Application starting",
 				logger.String("component", "bootstrap"),
 			)
 			return nil
 		},
-		OnStop: func(ctx context.Context) error {
+		OnStop: func(_ context.Context) error {
 			l.Info("Application shutting down",
 				logger.String("component", "bootstrap"),
 			)

internal/di/providers_test.go

@@ -16,9 +16,15 @@ func TestProvideConfig(t *testing.T) {
 
 	// Set environment variable
 	originalEnv := os.Getenv("ENVIRONMENT")
-	defer os.Setenv("ENVIRONMENT", originalEnv)
+	defer func() {
+		if err := os.Setenv("ENVIRONMENT", originalEnv); err != nil {
+			t.Logf("Failed to restore environment variable: %v", err)
+		}
+	}()
 
-	os.Setenv("ENVIRONMENT", "development")
+	if err := os.Setenv("ENVIRONMENT", "development"); err != nil {
+		t.Fatalf("Failed to set environment variable: %v", err)
+	}
 
 	// Create a test app with ProvideConfig
 	app := fx.New(
@@ -51,9 +57,15 @@ func TestProvideConfig_DefaultEnvironment(t *testing.T) {
 
 	// Unset environment variable
 	originalEnv := os.Getenv("ENVIRONMENT")
-	defer os.Setenv("ENVIRONMENT", originalEnv)
+	defer func() {
+		if err := os.Setenv("ENVIRONMENT", originalEnv); err != nil {
+			t.Logf("Failed to restore environment variable: %v", err)
+		}
+	}()
 
-	os.Unsetenv("ENVIRONMENT")
+	if err := os.Unsetenv("ENVIRONMENT"); err != nil {
+		t.Fatalf("Failed to unset environment variable: %v", err)
+	}
 
 	// Create a test app with ProvideConfig
 	app := fx.New(
@@ -240,7 +252,7 @@ func (m *mockConfigProvider) Get(key string) any {
 	return m.values[key]
 }
 
-func (m *mockConfigProvider) Unmarshal(v any) error {
+func (m *mockConfigProvider) Unmarshal(_ any) error {
 	return nil
 }
 
@@ -300,8 +312,8 @@ type mockLogger struct {
 	onStopCalled  bool
 }
 
-func (m *mockLogger) Debug(msg string, fields ...logger.Field) {}
-func (m *mockLogger) Info(msg string, fields ...logger.Field) {
+func (m *mockLogger) Debug(_ string, _ ...logger.Field) {}
+func (m *mockLogger) Info(msg string, _ ...logger.Field) {
 	if msg == "Application starting" {
 		m.onStartCalled = true
 	}
@@ -309,11 +321,11 @@ func (m *mockLogger) Info(msg string, fields ...logger.Field) {
 		m.onStopCalled = true
 	}
 }
-func (m *mockLogger) Warn(msg string, fields ...logger.Field)  {}
-func (m *mockLogger) Error(msg string, fields ...logger.Field) {}
-func (m *mockLogger) With(fields ...logger.Field) logger.Logger {
+func (m *mockLogger) Warn(_ string, _ ...logger.Field)  {}
+func (m *mockLogger) Error(_ string, _ ...logger.Field) {}
+func (m *mockLogger) With(_ ...logger.Field) logger.Logger {
 	return m
 }
-func (m *mockLogger) WithContext(ctx context.Context) logger.Logger {
+func (m *mockLogger) WithContext(_ context.Context) logger.Logger {
 	return m
 }