* perf(lint): keep JS plugins out of default oxlint and adopt ast-grep
Any jsPlugin makes Oxlint hand every file's AST to Node, so the seven custom
plugins cost the default `oxlint` run several times its native time.
- Move app-store-performance, quadratic-buffer-concat, renderer-scrollbar-style
and ime-enter-guard (scope- or dataflow-aware) to config/oxlint-js-plugins.json,
run by `pnpm lint:js-plugins`, CI, lint-staged and the changed-lines gate.
- Port sort-comparator-performance, mobile-pairing and native-chat-design-tokens
to ast-grep rules with rule tests, and delete the plugins.
- Add @ast-grep/cli, config/sgconfig.yml, `pnpm lint:ast-grep` / `test:ast-grep`,
a CI step, and an ast-grep pass in check-changed-code-quality.
- Add flaky-test rules (wall-clock reads, real-time waits, polling loops,
unquarantined skips, unexplained timeout bumps), baselined by a count ratchet.
* Enforce flaky-test ratchet on changed files; refresh baseline
* docs(agents): keep custom-rule details out of AGENTS.md
* Resolve ast-grep from the repo so gate scans of other roots work
Keep the rules most UI changes need in docs/STYLEGUIDE.md (32.9KB -> 10.1KB)
and move per-component specs, native chat scale, UX rationale, and the
screen review rubric into docs/styleguide/. Values now point at main.css
instead of being restated. Lint messages and comments that cited moved
sections now point at the new files.
Neil