Fix freshcodex transcript display turn contract

[danshapiro]

Summary:

• Normalize Freshcodex provider turns into stable display turns for transcript pages and bodies.
• Preserve send acknowledgements through submitted display turn ids and checkpoint metadata.
• Add restart-safe checkpoint matching for stale submitted turn links.

Verification:

• npm run test:vitest -- --config vitest.server.config.ts test/unit/server/fresh-agent/codex-adapter.test.ts test/unit/server/fresh-agent/codex-normalize.test.ts --run
• npm run test:vitest -- test/unit/client/lib/fresh-agent-checkpoints.test.ts test/unit/client/components/fresh-agent/FreshAgentView.test.tsx --run
• FRESHELL_TEST_SUMMARY="fresh agent transcript contract rebased before PR" npm run check