[codex] chore: upgrade to node 26

[ThomasK33]

Summary

• Upgrade the project Node toolchain from Node 25 to Node 26, locking mise to Node 26.1.0.
• Upgrade Playwright to 1.60.0, which includes the Node 26 install hang fix.
• Broaden documented and package engine support to >=24.0.0 <27.
• Add a Vitest setup hook that suppresses only Node 26's DEP0205 warning from tsx-spawned test child processes so stderr assertions stay meaningful.

Behavior impact

• Development and CI now run on Node 26.
• Runtime CLI behavior and public JSON contracts are unchanged.
• The test-only NODE_OPTIONS adjustment is scoped to Vitest child processes and does not affect the built CLI.

Validation

• mise run bootstrap-ci
• npx playwright install chromium
• npm run test -- test/integration/cli.test.ts test/e2e/renderer-slice.test.ts test/integration/evals/authoring-pilots.test.ts test/integration/release-scripts.test.ts
• mise run ci
• node dist/cli/main.js version --json
• AGENT_TTY_HOME=$(mktemp -d) node dist/cli/main.js doctor --json
• git diff --check