Improve Unity command discovery and preflight

[niqibiao]

Summary

• add a committed contract manifest for all 59 built-in Unity actions, grouped into 7 agent-facing domains and core/advanced/control-plane visibility tiers
• add offline, filtered command discovery and fail-closed preflight validation for recognized built-ins and batches while preserving custom-command pass-through
• reject malformed batch argument shapes while preserving the existing args/argsJson transport precedence
• hide the 2 non-verifiable UI commands from default discovery, tighten retry/timeout safety, and simplify the skill/docs around command-first routing
• keep public compatibility wording at Unity 2022

Why

The previous flow exposed the full command registry and deferred malformed or ambiguous requests to Unity. That increased routing ambiguity and allowed avoidable no-ops or partial mutations. The new committed contracts make the default discovery surface smaller and reject invalid arguments, selectors, mutation sentinels, session requirements, and unsafe ranges before HTTP dispatch.

Self-comparison effect

On the local 89-case offline routing proxy, strict micro accuracy improved from 71.9% to 100% (+28.1 percentage points). The improvement came from route, payload, and exposure-policy accuracy; activation classification remained 20/20 before and after, so this PR does not claim an activation-recall lift. A guarded run launched through UnityStart.cmd also completed 12/12 live Unity tasks with independent read-back and cleanup.

The local test files, comparison reports, and first-round research artifacts are intentionally not included in this PR.

Checks

• local regression suite — 46 passed
• live Unity contract run — 12/12 tasks passed; 59 calls across 27 routes; live registry matched all 59 committed IDs
• git diff --check