feat(review-tutor): add harness connector boundary

[ElbertePlinio]

What changed

• Added the harness connector boundary, Pi connector, explicit registry, and default-off connector flag.
• Namespaced model IDs while preserving legacy Pi model resolution.
• Generalized the shared runner without changing Pi argv, process limits, or lifecycle behavior.
• Added centralized child-failure redaction and harness/model export metadata.
• Added connector, registry, protocol, redaction, and runner regression coverage.
• Reverted root TypeScript and Vitest aliases; Review Tutor now imports the flags source directly.

Tested

• cd packages/review-tutor && npm run typecheck
• npx vitest run packages/review-tutor/test (278 passed)
• bun run check (569 passed, 25 skipped; coverage and builds passed)
• Full in-session contract, security, and process-boundary diff review; no actionable findings.

Not tested

• Real Pi, Claude Code, and Codex binaries were not run; all process tests use fakes.
• No user-visible UI behavior changed.
• Independent local-review lanes were unavailable in this harness, and provider binaries were explicitly out of scope.

Risk class

Serious backend (process + persistence boundary).

Refs #63

[ElbertePlinio]

Ready for human review at fb6a9cc. Panel: Opus (correctness) → P1/P2/P3 + KISS fixed and verified; Grok (security/process) clean; Sonnet (test integrity/conformance, substituted for the unauthenticated GLM lane) clean. Dismissed: bun.lock hunk is pre-existing peerDependency drift repaired by bun install. CI green. Stacked children: #77 (Claude Code), #78 (Codex).