Align mode catalog with ZCode 3.11.2 and add strict validation

[supermomonga]

Summary

Align the ACP adapter's mode catalog with ZCode 3.11.2's official modes and add strict validation to reject any modes outside the published catalog.

Changes

Mode Catalog

• Removed deprecated auto mode
• Updated mode names and descriptions to match ZCode 3.11.2 official UI
• Official modes: build (Ask before changes), edit (Edit automatically), plan (Plan mode), yolo (Full access)

Validation

• Added isZCodeModeId() type guard to validate client-provided mode IDs
• Added requireZCodeModeId() to validate native modes and reject protocol mismatches
• Reject unknown modes before calling the native host
• Reject invalid modes returned by native ZCode without changing session state

Refactoring

• Introduced updateBindingSnapshot() helper to centralize snapshot state updates
• Made MODE_OPTIONS const with TypeScript type narrowing for type safety
• Updated adapter spec and implementation status documentation

Testing

• All 61 tests pass (4 new tests added)
• Mode catalog validation: MODE_OPTIONS matches official ZCode 3.11.2 catalog
• Mode publishing: new/loaded/resumed sessions return correct modes and labels
• Mode switching: each official mode ID passed to host unchanged with current_mode_update notification
• Input rejection: unknown modes rejected with INVALID_CONFIGURATION error before calling host
• Native protocol errors: invalid modes from native ZCode rejected without changing session state
• Manual ACP wire verification: mode switching notifications, read tool, end_turn

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this closes #17