feat: add optional on-device transcript cleanup

[douglasjarquin]

Summary

• Adds an optional Clean mode backed by a fresh, short-lived on-device Foundation Models session.
• Instant mode inserts the finalized raw transcript without initializing Foundation Models.
• Clean mode persists raw.txt first, writes cleanup output separately to clean.txt, and falls back to raw text for unavailable, cancelled, timed-out, overflow, or failed cleanup.
• Adds sequential sentence/segment-aware chunking, protected technical-token validation, lifecycle metrics/signposts, and a versioned evaluation corpus.
• Adds Clean Again, Copy Clean, and Paste Clean Again History actions without changing durable audio or raw.txt.

Verification

• SwiftPM executable contract matrix for the spike and issues [02/13 · MVP] Build the native menu-bar shell and dictation state machine #3 through [07/13 · Intelligence] Add optional on-device transcript cleanup with raw fallback #8: passed.
• Native Xcode build with DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer: ** BUILD SUCCEEDED **.
• LSP diagnostics for changed Swift sources and contract harness: no diagnostics found.
• AppKit launch smoke check: menu-bar app reached Idle state and the exact process exited after capture.
• Foundation Models host probe: unavailable because appleIntelligenceNotEnabled.

Evidence limits and review receipt

• Real Foundation Models generation, production p95 latency, and memory-return measurement were unavailable on this host.
• Accessibility-driven History QA was blocked by macOS assistive-access error -1719; deterministic History contract coverage passed.
• The final exact-SHA review wave at 51af662344159def282dcfc246fc0d08ddc66160 returned Gate and context INCONCLUSIVE; QA, code, and security lanes were silent after bounded 120-second and 60-second closeout windows and were closed as INCONCLUSIVE.
• The parked no-mistakes run 01M04R4MP7VNKDGQZTPP6AHE05 remains cancelled at its stale reviewed head; custody returned to this branch and no fresh run was started per the bounded closeout instruction.
• Cleanup is intentionally in-process and structured. Foundation Models cancellation is expected to be cooperative; an arbitrary injected non-cooperative model could delay the raw fallback, and issue [10/13 · Performance] Enforce resource budgets and lifecycle release gates #11 prohibits adding a helper process as a workaround.

Closes #8