migrate from yarn 1 to pnpm

- switch root package manager to pnpm 10.33.4 via packageManager field
- add .npmrc with node-linker=hoisted for RN/Expo compatibility
- convert yarn resolutions to pnpm.overrides; pin psl@1.9.0 and @types/psl@1.1.1
  to keep types resolving under exports-aware resolution
- pin react-compiler-runtime and babel-plugin-react-compiler to real rc.3 (the
  deprecated "Wrong version name was published" tag would otherwise resolve)
- add pnpm.onlyBuiltDependencies allowlist for @sentry/cli, core-js-pure,
  esbuild, unrs-resolver
- regenerate pnpm-lock.yaml; delete yarn.lock; drop postinstall-postinstall
- update all workflows, Dockerfile, Dockerfile.embedr (root-level), Makefile,
  conductor.json; bskyembed/bskylink/bskyogcard/dev-env stay on yarn
- update docs (CLAUDE.md, docs/build.md, docs/testing.md, docs/localization.md,
  bskyweb/README.md, scripts/push-notification/README.md, BlueskyClip/README.md)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/nightly-update-source-languages.yaml

@@ -19,19 +19,20 @@ jobs:
         uses: actions/checkout@v4
         with:
           ssh-key: ${{secrets.GH_ACTION_DEPLOY_KEY}}
+      - uses: pnpm/action-setup@v4
       - name: Install node
         uses: actions/setup-node@v6
         with:
           node-version-file: .nvmrc
-          cache: yarn
-      - name: Yarn install
+          cache: pnpm
+      - name: pnpm install
         uses: Wandalen/wretry.action@master
         with:
-          command: yarn --frozen-lockfile
+          command: pnpm install --frozen-lockfile
           attempt_limit: 3
           attempt_delay: 2000
       - name: Extract language strings
-        run: yarn intl:extract
+        run: pnpm intl:extract
       - name: Create commit
         uses: stefanzweifel/git-auto-commit-action@v5
         with: