Implement one-instruction contract compiler

[chriswu727]

What changed

• added bounded read-only repository discovery and a typed one-instruction acceptance contract compiler
• added an independent critic plus deterministic risk, confidence, capability, command-policy, artifact, and coverage gates
• SHA-256 locks accepted contracts before mutation and verifies the lock on resume
• preserves Advanced user checks, supports clarification/recompile, and binds the contract into Receipts, replay, and Apply/Undo
• simplified the default UI to project + instruction, with contract provenance and Advanced controls
• added the migration, ADR/strategy/README updates, deterministic end-to-end coverage, and a real-provider flagship evaluation fixture

Why

Loop's flagship promise is that a user can hand off a real repository with one instruction. The previous strict path required the user to manually author criteria, checks, artifacts, capabilities, and budgets, which shifted orchestration back to the user.

Verification

• 437 backend tests
• Python Ruff, formatting, and MyPy
• web lint, typecheck, 18 tests, and production build
• desktop lint, typecheck, 14 tests, and build
• Alembic 0008 → 0009 → 0008 → 0009 round trip
• in-app browser interaction and console check
• targeted Prettier and git diff checks

A real-provider Gate 1 result is intentionally not claimed because no provider key was available in this environment. The committed evaluator is ready to produce that evidence.