fix(tools): tolerate description=null in real KeeperHub catalogue

[devin-ai-integration]

Summary

After PR #1 landed and the production server was restarted from main,
the auto-generated tool catalogue collapsed to just the 5 static tools
(it had been 23 — 5 static + 18 from the live KeeperHub catalogue).

Root cause: a real KeeperHub workflow entry now has description: null
in its listing. build_workflow_tools() was calling .strip() on that
None, the entire builder threw, and the server's exception-fallback in
_build_tool_specs() quietly swallowed it.

Fix: coerce description / name through str() with the slug as the
final fallback. Added a regression test using a synthetic mock
catalogue with description: null and name: null.

Review & Testing Checklist for Human

Risk: green — 6-line bug fix in one function plus a new test.

• Confirm pytest -q shows 31 passing tests (was 30).
• After merge, tool_count on http://178.104.45.97:8420/api/health
  should jump back from 5 to ~23 once we pull and restart.

Notes

The exception-swallowing fallback was working as designed (the server
stays up with degraded tool surface even when discovery breaks), but
silently — there's no current log line warning that we fell back. If
you'd like, a follow-up could add a logger.warning("catalogue discovery failed: %s — falling back to static tools", exc) call in
_build_tool_specs() so this kind of issue surfaces in journalctl.

Link to Devin session: https://app.devin.ai/sessions/4c74607caacb488d803b3a14a74ee6df
Requested by: @danilaverbena

[devin-ai-integration]

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