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/logger/middleware_test.go

@@ -80,7 +80,7 @@ func TestRequestIDFromContext(t *testing.T) {
 	}{
 		{
 			name:      "with request ID",
-			ctx:       context.WithValue(context.Background(), RequestIDKey(), "test-id"),
+			ctx:       context.WithValue(context.Background(), requestIDKey, "test-id"),
 			want:      "test-id",
 			wantEmpty: false,
 		},
@@ -92,7 +92,7 @@ func TestRequestIDFromContext(t *testing.T) {
 		},
 		{
 			name:      "with wrong type",
-			ctx:       context.WithValue(context.Background(), RequestIDKey(), 123),
+			ctx:       context.WithValue(context.Background(), requestIDKey, 123),
 			want:      "",
 			wantEmpty: true,
 		},
@@ -160,7 +160,7 @@ func TestUserIDFromContext(t *testing.T) {
 	}{
 		{
 			name:      "with user ID",
-			ctx:       context.WithValue(context.Background(), UserIDKey(), "user-123"),
+			ctx:       context.WithValue(context.Background(), userIDKey, "user-123"),
 			want:      "user-123",
 			wantEmpty: false,
 		},
@@ -172,7 +172,7 @@ func TestUserIDFromContext(t *testing.T) {
 		},
 		{
 			name:      "with wrong type",
-			ctx:       context.WithValue(context.Background(), UserIDKey(), 123),
+			ctx:       context.WithValue(context.Background(), userIDKey, 123),
 			want:      "",
 			wantEmpty: true,
 		},
@@ -303,7 +303,7 @@ func TestRequestIDMiddleware_MultipleRequests(t *testing.T) {
 func TestSetRequestID_Overwrite(t *testing.T) {
 	t.Parallel()
 
-	ctx := context.WithValue(context.Background(), RequestIDKey(), "old-id")
+	ctx := context.WithValue(context.Background(), requestIDKey, "old-id")
 	newCtx := SetRequestID(ctx, "new-id")
 
 	requestID := RequestIDFromContext(newCtx)
@@ -315,7 +315,7 @@ func TestSetRequestID_Overwrite(t *testing.T) {
 func TestSetUserID_Overwrite(t *testing.T) {
 	t.Parallel()
 
-	ctx := context.WithValue(context.Background(), UserIDKey(), "old-user")
+	ctx := context.WithValue(context.Background(), userIDKey, "old-user")
 	newCtx := SetUserID(ctx, "new-user")
 
 	userID := UserIDFromContext(newCtx)
@@ -350,10 +350,10 @@ func (m *mockLoggerForMiddleware) Error(msg string, fields ...logger.Field) {
 	m.logs = append(m.logs, logEntry{message: msg, fields: fields})
 }
 
-func (m *mockLoggerForMiddleware) With(fields ...logger.Field) logger.Logger {
+func (m *mockLoggerForMiddleware) With(_ ...logger.Field) logger.Logger {
 	return m
 }
 
-func (m *mockLoggerForMiddleware) WithContext(ctx context.Context) logger.Logger {
+func (m *mockLoggerForMiddleware) WithContext(_ context.Context) logger.Logger {
 	return m
 }