feat(pi): submit plans from any mode

[CodeByPeete]

Summary

• keep plannotator_submit_plan available while Plannotator is idle, planning, or executing
• preserve the existing transition into execution when a planning-phase submission is approved
• treat submissions from idle or executing as review-only, leaving the current phase and tracked plan unchanged

Validation

• bun test ./apps/pi-extension/tool-scope.test.ts ./apps/pi-extension/submit-plan-runtime.test.ts
• bunx tsc --noEmit -p apps/pi-extension/tsconfig.json

The focused suite passes 10 tests. The Pi extension suite reaches 58 passing tests. Existing Windows-only semantic-diff executable and locked temporary-directory failures remain outside this change.

[backnotprop]

Heads up: this conflicts with #1124, which lands first. This branch keeps the snapshot restore that #1124 removes, so it reintroduces the clobbering bug. After #1124 merges, please rebase and express submit-from-any-mode under its tracking model (keep the submit tool out of phaseAddedTools rather than restoring snapshots).