Coverage priorities 1-5: test pure functions, extract interfaces, mock-based handler tests

- Priority 1: Test NewSendEmailTask + NewSendPushTask (5 tests)
- Priority 2: Test customHTTPErrorHandler — all 15+ branches (21 tests)
- Priority 3: Extract Enqueuer interface + payload builders in worker pkg (5 tests)
- Priority 4: Extract ClassifyFile/ComputeRelPath in migrate-encrypt (6 tests)
- Priority 5: Define Handler interfaces, refactor to accept them, mock-based tests (14 tests)
- Fix .gitignore: /worker instead of worker to stop ignoring internal/worker/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/models/user_test.go

@@ -11,10 +11,10 @@ import (
 func TestUser_SetPassword(t *testing.T) {
 	user := &User{}
 
-	err := user.SetPassword("testpassword123")
+	err := user.SetPassword("testPassword123")
 	require.NoError(t, err)
 	assert.NotEmpty(t, user.Password)
-	assert.NotEqual(t, "testpassword123", user.Password) // Should be hashed
+	assert.NotEqual(t, "testPassword123", user.Password) // Should be hashed
 }
 
 func TestUser_CheckPassword(t *testing.T) {