Fix Windows Stop UI synchronization

[coneilen]

Summary

Fix the Windows shell's stale Stop UI after the daemon successfully stops a loop. The shell now decodes the Swift daemon's synthesized LoopState object payload instead of silently replacing it with idle.

Changes

• decode every supported daemon loop state from both production object payloads and legacy string fixtures
• reject unknown or malformed populated state objects without replacing the current graph
• cover an already-open terminal workspace receiving stopped, retaining its selected node, and removing the Stop control

Test plan

RED: zig test src\App.zig --test-filter "open workspace applies production stopped state" -> expected stopped, found idle; 0 passed, 1 failed
GREEN: zig test src\App.zig --test-filter "open workspace applies production stopped state" -> All 1 tests passed
REGRESSION: zig test src\App.zig with native provider/link inputs -> All 773 tests passed

• zig test src\GraphModel.zig -> All 155 tests passed
• Tools\windows\validate.ps1 -Task windows-shell -ShellPart integration -SkipTrayLive -ShellValidationRoot C:\v -> passed; live shell/UIA integration and REAL_DAEMON_ROUNDTRIP: PASS
• No shared Swift or macOS production files changed, so no macOS build was run.

Checklist

• I have read the Contributing Guidelines
• I have signed off my commits (git commit -s) per the DCO
• Tests pass locally (make test)
• Code follows the existing style (make check)
• I added the test/contract before the implementation and observed the intended RED failure