v0.3.0 — ?refresh + 429 in OpenAPI + /rates/ta uses bars cache

Closes the three deferred items from v0.2.0:

1. `?refresh=true` query param threaded through 24 cacheable
   operations. Bypasses the cache read, still writes the fresh
   result back. Default false — caching stays transparent.

2. `429 RATE_LIMIT_NEAR` documented in OpenAPI on every IBKR-bound
   operation. Body shape unchanged from v0.2.0 runtime behavior;
   clients can now discover it via /openapi.json instead of having
   to be told.

3. /rates/ta endpoints split into bars-via-cache + ta_enrich. Cache
   hits = zero IBKR load + fresh wickworks indicators. Every TA
   call also grows the goldmine.

Stack: Python 3.12 + FastAPI + ib_async + Linux-native IB Gateway.
142 tests pass. ruff + bandit + pip-audit + audit-compose all
clean at release.

Generated clients import paths:
  Go:     github.com/psyb0t/ibkr-httpapi/pkg/clients/go
  Python: pip install "git+https://github.com/psyb0t/ibkr-httpapi.git@v0.3.0#subdirectory=pkg/clients/python/ibkr-httpapi-client"