chore(lint): migrate to oxlint and oxfmt - #1117

Replace `{value && <Element />}` with ternaries in the four places the
left-hand operand is not provably boolean.

`@eslint-react/no-leaked-conditional-rendering` flagged non-boolean
operands here, but it requires type information, so it cannot run as an
Oxlint JS plugin. It also only reports number, bigint, and NaN operands:
strings and plain booleans are allowed on React 18 and later, so these
four sites were already safe. Making them explicit keeps the intent
obvious and means dropping the rule costs no coverage.

Replace Prettier with Oxfmt for formatting and drop the `--cache` flags,
which Oxfmt does not support.

`.oxfmtrc.json` comes from `oxfmt --migrate prettier`, which reads
`.prettierrc.json` and `.prettierignore` and preserves the verbatim-write
exclusions for golden snapshots and generated VS Code themes. The
`*.jsonc` override could not be migrated automatically and is written by
hand. `printWidth` stays at 80 to match the previous output. `sortImports`
is left off: it reorders imports differently from `import-x/order` and is
not a drop-in.

This reformats 22 files. Both differences are formatting-only, and output
is deterministic and idempotent:

- Union types are expanded to leading-pipe style. This is a known
  divergence, oxfmt currently matches Prettier 3.4 rather than 3.9
  (oxc-project/oxc#25841).
- One `yield` operand in `src/telemetry/export/writers/json.ts` is wrapped
  in parentheses.

Prettier stays a devDependency: Oxfmt delegates Markdown, HTML, YAML, and
Vue to it internally, and the residual ESLint config still formats against
it.

Use TypeScript 7 for typechecking while keeping the TypeScript 6 API
available to typescript-eslint, which refuses to load against TypeScript 7
(its peer range is `>=4.8.4 <6.1.0`, and support is still tracked upstream).

Following the official side-by-side guidance:

- `typescript` is aliased to `@typescript/typescript6`, which re-exports the
  6.0 API that typescript-eslint consumes. Its binary is `tsc6`.
- `@typescript/native` is aliased to `typescript@^7`, providing the `tsc`
  binary used by `pnpm typecheck` and editors.

Measured on this repo: typechecking the root config drops from 1701ms to
371ms, and the test config from 3768ms to 903ms.

tsgolint already embeds the TypeScript 7 engine, so Oxlint's type-aware
rules were already running on it; this brings `pnpm typecheck` onto the same
engine. When TypeScript 7 ships an API, drop `@typescript/native` and point
`typescript` back at a single version.

Both tools default to one thread per core. Thread startup is a fixed
per-thread cost, so on machines with many cores it outweighs the parallelism
it buys. Measured on this repo (511 files) on a 128-core machine:

| | default | capped |
| --- | --- | --- |
| oxlint --type-aware | 4.0s | 2.1s |
| oxfmt --check | 1.8s | 0.23s |

Degradation starts above roughly 32 cores. From 2 to 16 cores the cap makes
no measurable difference, because the default already equals it, and CI
runners (4 vCPU) detect 4 either way, so this only affects large dev boxes.

The value is capped rather than pinned, so smaller machines and CI keep
their own optimal thread count instead of being pushed into an
oversubscribed one. A fixed number would have made a 2-core machine 1.6x
slower.

The helper script is run through Node rather than a `$(...)` substitution in
the npm scripts, so it behaves identically on Windows.

Warm `pnpm lint` drops from 4.5s to 2.9s and `pnpm format:check` from 1.8s
to 0.31s. Upstream tracking: oxc-project/oxc#21672.

Tighten the wording added in the oxlint/oxfmt migration: drop em-dashes,
trim wordy sentences, and shorten the thread-cap comment in run-oxc.mjs
to the load-bearing facts.

Fix the TypeScript 7 announcement URL in CONTRIBUTING.md, which was
missing the /typescript/ path segment.

- Remove comments from .vscode/settings.json
- Condense comments in packages/ui/tsconfig.json and pnpm-workspace.yaml
- Use block comments in scripts/run-oxc.mjs
- Document why sortPackageJson is disabled in .oxfmtrc.json
- Drop ignorePatterns for paths nothing generates (.nyc_output, .claude,
  pnpm-debug.log)
- Remove redundant empty rules object from .oxlintrc.json
- Slim test/unit/oxlintConfig.test.ts by inlining single-use helpers
- Trim the eslint-plugin-oxlint implementation detail from AGENTS.md

Switch .oxlintrc.json from an explicit 59-rule list to
categories.correctness: error, keeping only the 7 rules not in the
category. This enables 36 additional rules; fix the 5 findings:

- treeTransition.ts: spread on string breaks emoji code points
- cliManager.ts: spread on AxiosHeaders loses class prototype
- deploymentManager.test.ts, loginCoordinator.test.ts: spread on class
  in vi.mock drops prototype
- localJsonlSink.test.ts: toSorted() without comparator sorts
  lexicographically

Extract the react/react-x override into .oxlintrc.react.json via
oxlint extends.