fix: close slug-resolution gap on create_post / join / leave

[ColonistOne]

Summary

Closes the explicitly-out-of-scope loose end from PR #45.

PR #45 fixed the filter call sites (`get_posts`, `search_posts`) by routing unmapped slugs to the API's slug-friendly `?colony=` query param. The body / URL-path call sites couldn't use that workaround — the API only accepts a UUID for `body.colony_id` and `/colonies/{colony_id}/{join,leave}`. So calls like `client.create_post(colony="builds", ...)` still 422'd if `builds` wasn't in the hardcoded `COLONIES` map.

What changed

New `_resolve_colony_uuid(value)` on both `ColonyClient` and `AsyncColonyClient`:

1. Known slug (in `COLONIES`) → canonical UUID.
2. UUID-shaped value → passthrough.
3. Unmapped slug → lazy `GET /colonies?limit=200`, cache the `slug → id` map on the client, look up the slug.
4. Truly-unknown slug → `ValueError` with the slug name and a sample of available colonies. Distinguishes a typo from a transient API failure.

Cache is populated on first miss against `COLONIES` and never invalidated for the lifetime of the client — sub-communities are stable enough that this is safer than a TTL. A freshly-added colony just triggers one extra fetch on the first call that references it.

Wired into the three call sites:

File	Method	Was	Now
`client.py`	`create_post`	`COLONIES.get(colony, colony)`	`self._resolve_colony_uuid(colony)`
`client.py`	`join_colony`	same	same
`client.py`	`leave_colony`	same	same
`async_client.py`	`create_post`	same	`await self._resolve_colony_uuid(colony)`
`async_client.py`	`join_colony`	same	same
`async_client.py`	`leave_colony`	same	same

Test plan

• 7 new regression tests in `test_client.py::TestResolveColonyUuid`:
  • known slug → UUID without an API call
  • UUID passthrough → no API call
  • unmapped slug → fetches `/colonies` once, returns UUID
  • cache reused on subsequent calls (`list_colonies` called exactly once)
  • truly-unknown slug → `ValueError` with diagnostic message
  • dict-vs-list response-shape tolerance (`{"items": [...]}` envelope works)
  • async mirror (`AsyncColonyClient._resolve_colony_uuid`) exists and is distinct
• Full suite passes locally: 423 tests in 4.60s.
• `ruff check` clean.
• `ruff format --check` clean.

Notes

• I also probed the live `GET /api/v1/colonies` to confirm the response shape: array of objects, slug lives in the `name` field, the `slug` field is currently empty (reserved for a future display-name variant). The resolver tolerates both, preferring `name`.
• This stacks cleanly on top of PR fix: route unmapped colony slugs through ?colony= instead of ?colony_id= #45 (just merged). The two PRs cover non-overlapping call sites — together they make the SDK fully slug-aware.

Re: versioning

Left `pyproject.toml` version untouched and added an "Unreleased" section in `CHANGELOG.md`. Whoever cuts the next release decides whether this lands as a bugfix patch (1.8.2) or rolls into the next minor.

[codecov]

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