chore: clean up .gitignore and remove unused output.zip

[rajarshidattapy]

Addresses #592, items 1 and 2. Item 3 is answered below but deliberately unchanged, so this
does not auto-close the issue.

Change

output.zip | deleted (0 bytes)
.gitignore | -3   dead .speakeasy patterns + misleading comment

output.zip — unreferenced anywhere in the repo; grep across the tree returns nothing, and
its only commit is the Copybara import (5f2c0ee).

.gitignore — checked both directions before removing the two patterns. All four tracked
files match them (gen.lock, workflow.lock, in.openapi.yaml, out.openapi.yaml), and
git status --ignored confirms the patterns are currently hiding zero untracked files. So
removing them changes no ignore behaviour; it only stops the file from implying those artifacts
aren't committed here. The neighbouring .speakeasy/temp/, .speakeasy/logs/, and
.speakeasy/reports rules cover genuinely untracked output and are untouched.

Item 3: the /messages exclusion — no change, and I'd argue there shouldn't be

Two findings while checking it.

The exclusion is deliberate and owned upstream. x-speakeasy-ignore: true is present in
in.openapi.yaml, not added by any local overlay — it comes from the monorepo spec. That
settles the "worth confirming" question without needing a maintainer.

Given that, both suggested cleanups would be net-negative:

• x-speakeasy-name-override: 'create' is not dead weight, it is load-bearing if the
  exclusion is ever lifted — it is exactly what makes the namespace client.messages.create.
  Stripping it via an overlay would sabotage a future un-ignoring.
• The orphaned Anthropic Messages tag produces no artifact: no docs/sdks/ directory, no
  docs.json nav entry, no SDK class. Removing it would mean adding and maintaining a new
  overlay for zero observable change.

One correction to the issue's premise. "We ship the types for an endpoint the client can't
call" isn't accurate. All 8 messages* component modules are consumed by presets.py —
presets.create_presets_messages takes components.MessagesRequest,
MessagesMessageParam, MessagesRequestToolUnion, MessagesFallbackParam,
MessagesOutputConfig and friends. They serve a callable endpoint; they just are not reachable
through a client.messages namespace.

What remains in item 3 is the product question — should /messages be exposed at all — and
that is a monorepo spec decision rather than something this repo can settle.

Verification

• uv build produces both sdist and wheel
• test suite: 3 passed, 1 failed — the failure is
  test_responses_namespace.py::test_responses_namespace_is_ga_and_beta_alias_remains_available,
  which is Test suite is red on main and CI never runs it: pytest is in neither the dev group nor pr-validation.yaml #585 and already red on main before this branch.