chore: finish beta production readiness

[Abhirup0]

What changed?

Finishes the automatable 0.4.0-beta.1 production-readiness work:

• real PTY crash/switch/resize/terminal-restoration checks on Linux, macOS, and Windows
• all-game render/resize performance budgets and coverage regression floors
• type-aware linting and repository formatting policy
• developer clone/install/cancellation/registry/description safety tests
• prerelease-safe npm beta dist-tag selection
• updated beta support language, changelog, contributor gate, and living readiness status

The original workspace's two existing JSON deletions were intentionally excluded.

Local verification

• clean npm ci
• npm run prepublishOnly (60 files, 247 tests)
• npm run coverage (all thresholds pass)
• 20/20 playtest profiles at 80x24
• package: 1,370,123 bytes packed / 5,852,720 unpacked
• render p95: 91.2 ms startup / 3.8 ms resize
• release tag verification selects npm beta
• git diff --check

The local npm advisory endpoint reset its connection; GitHub's production audit, scheduled/full audit policy, and dependency review remain fail-closed remote gates.

Human and policy boundary

This PR does not claim stable production readiness. Independent terminal/usability/accessibility sessions, 48-hour beta observation, license-expression choice, and least-privilege site credentials remain explicit external gates.