gitea: move workflows to .gitea, disable caches; settle the keystroke flake

Gitea prep: .github becomes .gitea (the act runner looks there), and
every actions/cache + Swatinem/rust-cache step is commented out until
the self-hosted instance has a cache provisioned. The remaining
marketplace actions (checkout/upload-artifact are act-compatible;
msys2/setup-msys2, dtolnay/rust-toolchain and softprops/action-gh-release
need a runner test / replacement) are a follow-up.

tests: the two gpui keystroke tests that flaked on Windows CI (undo
pair, snapping toggle — each once, values identical to the pass state,
Global-route keys) now dispatch each key with a double park. The root
cause is not fully pinned: the loss happens inside gpui's synthetic
key dispatch on Windows (both tests hold every test lock; production
is unaffected). The CI retry-once remains the backstop. The earlier
idea of advancing the simulated clock to flush gpui's pending-input
timer is off the table: the mock engine's playback ticks with executor
time, so a clock advance moves the playhead out from under the
assertions (observed: playhead 14 vs expected 9).

.github/actionlint.yaml

@@ -1,7 +0,0 @@
-# actionlint configuration: whitelist the custom self-hosted runner labels
-# used by the CD workflow (Warp.dev runners) so `actionlint cd.yml` passes.
-# See https://github.com/rhysd/actionlint/blob/main/docs/config.md
-self-hosted-runner:
-  labels:
-    - ubuntu-latest
-    - windows-latest