chore(tests): consolidate duplicated mcp_tool_capture pattern across vertical test files

[dougborg]

Problem

frontapp_mcp_server/tests/conftest.py already defines a shared mcp_tool_capture fixture (a factory that registers a tools module against a fake FastMCP and returns the captured {name: callable} dict). However, five existing per-vertical test files still define their own copy of the same pattern locally:

• tests/test_contacts_tools.py
• tests/test_drafts_tools.py
• tests/test_messages_tools.py
• tests/test_tags_tools.py
• tests/test_inboxes_tools.py

The conftest comment captures the intent:

Existing per-vertical test files (test_contacts_tools, test_drafts_tools, test_messages_tools, test_tags_tools, test_inboxes_tools) still define their own copy of the same pattern — migration is tracked as follow-up cleanup so this PR doesn't churn 5 working test files.

This issue is that follow-up cleanup.

Plan

1. For each of the 5 files, replace the local FakeMCP/captured-dict scaffolding with the shared mcp_tool_capture fixture from conftest.py
2. Remove the local class definitions
3. Update fixture lists in the affected tests
4. Keep the test bodies unchanged — only the setup-fixture wiring changes

Acceptance criteria

• Five test files no longer define FakeMCP or local capture dicts
• All tests pass (uv run poe test)
• No regression in test count (currently 610 passing)
• Conftest comment about "follow-up cleanup" can be removed

Note

This is a no-functional-change refactor; expected to be a small focused PR. Likely a half-hour of mechanical work but worth tracking so it doesn't bit-rot.

Reference

• frontapp_mcp_server/tests/conftest.py:96-127 — the shared factory and the comment about pending migration