[codex] Polish app-server APIs and examples

[jrkropp]

Summary

Polishes codex-js as a Codex-aligned SDK and replaces the old examples with a canonical local Node example plus a by-the-book Cloudflare Worker + Durable Object + Vite React example.

What Changed

• Added stable server helpers in @jrkropp/codex-js/server:
  • createCodexAppServer
  • createCodexAppServerConnection
  • defineDynamicTool
  • defineDynamicToolset
  • dynamicToolResponse
  • pending server-request and connection snapshot contracts
• Added dynamic tool validation and server-executed tool auto-resolution while preserving client-resolved tool escape hatches.
• Added app-server connection snapshot support for reconstructable runtimes, including Durable Object WebSocket hibernation use cases.
• Renamed internal bespoke_event_handling terminology to app_server_event_mapping.
• Replaced the previous examples with:
  • examples/node-local: local Vite + Node WebSocket app-server example.
  • examples/cloudflare: Vite React + Cloudflare Worker + Durable Object example with one-time WebSocket tickets, SQLite-backed thread state, hibernating WebSockets, and dynamic tools.
• Uses Cloudflare's standard secret handling for the example: .dev.vars locally, wrangler secret put for deploys, generated Worker types, and secrets.required in Wrangler config.
• Moved internal parity/mirror/reference docs out of package roots and updated public READMEs around the intended developer path.
• Added real static linting with ESLint.
• Bumped both packages to 0.3.0 for the pre-1.0 API/example polish release.

Validation

• pnpm check
• pnpm release:preflight
• NPM_TOKEN=local-preflight pnpm release:preflight
• pnpm --filter @jrkropp/codex-js-cloudflare-example cf:types:check
• pnpm --filter @jrkropp/codex-js-cloudflare-example typecheck
• pnpm --filter @jrkropp/codex-js-cloudflare-example test
• pnpm --filter @jrkropp/codex-js-cloudflare-example deploy:dry-run

Release Notes

No changeset file is included because package versions are already set to 0.3.0 and both published npm packages are currently below that version. The main release workflow should publish @jrkropp/codex-js@0.3.0 and @jrkropp/codex-js-react@0.3.0 directly after this lands.