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>

.claude/settings.local.json

@@ -12,7 +12,9 @@
       "Bash(git add:*)",
       "Bash(docker ps:*)",
       "Bash(git commit:*)",
-      "Bash(git push:*)"
+      "Bash(git push:*)",
+      "Bash(docker info:*)",
+      "Bash(curl:*)"
     ]
   },
   "enableAllProjectMcpServers": true,