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>

modules/BlueskyClip/README.md

@@ -126,9 +126,9 @@ modules/BlueskyClip/
 
 ## Development Notes
 
-- The App Clip is built as part of the main Xcode project when running `yarn prebuild`
+- The App Clip is built as part of the main Xcode project when running `pnpm prebuild`
 - Source files are copied during the prebuild process, not directly referenced
-- Changes to Swift files require running `yarn prebuild` to take effect
+- Changes to Swift files require running `pnpm prebuild` to take effect
 - The App Clip shares the same version number as the main app
 - App Clips have a 15MB size limit (enforced by Apple)
 - Users can convert an App Clip session into a full app install without losing data (via shared App Group)