ci(async-audit): wire async-route audit hook in disabled state (Phase 1)

[pcalnon]

Summary

Phase 1 wiring of the async-route audit hook (BUG-JD-10 class
prevention) for juniper-data. Adds a ruff-based pre-commit hook
scoped to the `ASYNC` ruleset, stage-restricted to `manual`
so it doesn't fire on regular commits.

First of four Phase 1 wiring PRs. Order per the migration plan
(`ASYNC_ROUTE_AUDIT_HOOK_MIGRATION_PLAN.md`
§4): data → cascor → canopy → worker.

What's added

```yaml

• id: ruff
  alias: ruff-async-audit
  name: Async-route audit (BUG-JD-10 class)
  args: [--select, ASYNC, --exit-zero]
  files: ^juniper_data/.*\.py$
  stages: [manual]
  ```

• `alias: ruff-async-audit` lets us reference the hook
  independently of the existing `ruff` and `ruff-format` hooks
  for invocation and Phase-2 enablement.

• `--exit-zero` means violations are reported but don't fail
  the hook in Phase 1 (the disabled-state contract).

• No `pyproject.toml` change — `[tool.ruff.lint] select` stays
  unchanged so regular runs don't enforce `ASYNC` yet.

• No CI workflow change in this PR; CI lane lands in Phase 2.

How to use

```bash

Show the 3 enumerated violations on demand:

pre-commit run --hook-stage manual ruff-async-audit --all-files
```

Verified locally to surface all 3 violations from the Phase 0
enumeration (`juniper_data/api/app.py:46`, `juniper_data/api/routes/health.py:131` and `:132` — all `ASYNC240` pathlib-in-async).

What's next

• Phase 2 (next, this repo): flip `stages` to
  `[pre-commit, manual]`, add CI lane with
  `continue-on-error: true`.
• Phase 3: fix the 3 production violations (estimated 30 min
  per the Phase 0 doc).
• Phase 4: flip CI lane to hard-fail; add hook to active
  pre-commit stages.

Test plan

• `pre-commit run --hook-stage manual ruff-async-audit --all-files`
  surfaces 3 violations (no false positives, no missed sites).
• Regular `pre-commit run` does NOT fire the new hook —
  verified by running on `juniper_data/api/routes/health.py`
  and confirming only `ruff` and `ruff-format` ran.
• No code changes; pre-commit config only.

🤖 Generated with Claude Code

[pcalnon]

approved