refactor(api): split buzz/api into typed domain packages

[harshtandiya]

The per-PR backport flow stalled after #294, so main is missing the whole buzz/api refactor
series plus the CI work that went with it. The individual backport PRs (#304, #306) were closed
rather than merged, and cherry-picking the rest one at a time doesn't work — everything from #296
onward edits the package layout that #295 created, so each one conflicts without its base.

Batching them into a single PR instead. git log --cherry-pick --left-only main...develop is
empty — every commit on main already has a patch-equivalent on develop — so this is a content
superset, not a merge exercise.

Pointing the branch at develop HEAD directly still conflicted, though: the merge base is
c6cb341, and because past backports landed on main as fresh cherry-picks, a three-way merge
sees both sides adding the same changes (buzz/api/forms.py reads as "deleted in develop, modified
in main"). None of it is real divergence. So this branch is one commit parented on main whose
tree is byte-identical to develop at a4f52b2 — git diff <branch> develop is empty. Since it
squash-merges anyway, main ends up with exactly the same commit either way.

What lands (109 files, +5751 / −2524), folding in:

Commit	PR
a08b6c7	#273	ci: add label-driven backport workflow
7094813	#291	ci: keep backport PR titles conventional
66396ad	#295	refactor: split buzz/api into domain packages
11e7d6f	#296	refactor(api): add response schemas to the thin domains
30c6698	#297	refactor(api): check-in service class + typed responses
14cecdc	#298	refactor(api): sponsorships service class, payments cleanup
8f7653d	#300	refactor(api): split forms into fields/services
e218c1e	#301	refactor(api): split tickets into windows/services
36eb7bf	#305	ci: shared bench setup action, stop evicting browser cache
6de3cd0	#302	refactor(api): split booking into services/guests
a4f52b2	#303	refactor(api): enforce type annotations on whitelisted methods

Worth knowing before merging:

• buzz/hooks.py has two live changes: require_type_annotated_api_methods = True, and the app
  screen's has_permission moves to buzz.api.account.has_app_permission. Deployments tracking
  main need a bench migrate + restart to pick up the new path.
• buzz.api.* import paths change shape. In-repo callers are all carried here; anything outside
  this repo importing buzz.api.<name> directly will break.
• ci.yml and ui-tests.yml are rewritten around the new .github/actions/setup-bench composite
  action, so this PR is validating its own CI changes.

No schema patches, no version bumps, no dependency changes — patches.txt, pyproject.toml and
both package.json files are untouched. Squash-merging to keep main's one-commit-per-backport
history.

[greptile-apps]

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