chore: replace biome with oxc (oxfmt + oxlint)

- Remove @biomejs/biome from root and packages/expo-two-way-audio
- Delete biome.json
- Add .oxfmtrc.json (migrated from biome via oxfmt --migrate=biome)
- Add .oxlintrc.json with curated rule set: react, react-perf,
  react-hooks, typescript, unicorn, oxc, import, promise
  - Rules target functional gotchas, untyped code, perf issues,
    deep JSX, nested ternaries, complexity, unused code
  - Noisy stylistic rules explicitly disabled
- Add npm scripts: lint, lint:fix (oxfmt replaces format/format:check)
- Update CI to run oxfmt --check

Lint is wired up but not enforced — all rules at warn. Baseline:
6040 warnings, 0 errors.

.oxfmtrc.json

@@ -0,0 +1,15 @@
+{
+  "$schema": "./node_modules/oxfmt/configuration_schema.json",
+  "useTabs": false,
+  "tabWidth": 2,
+  "printWidth": 100,
+  "singleQuote": false,
+  "jsxSingleQuote": false,
+  "quoteProps": "as-needed",
+  "trailingComma": "all",
+  "semi": true,
+  "arrowParens": "always",
+  "bracketSameLine": false,
+  "bracketSpacing": true,
+  "ignorePatterns": ["*.lock"]
+}