Stabilize full-mode playback UI and auto-enable taskbar widget

[ieproject-app]

Summary

• improve full-mode stability by adding timeline state (has_timeline, position_ms, duration_ms) from host to deskband
• replace full-mode moving title marquee with elapsed/duration progress text path and per-second repaint updates
• reduce stale transition windows on track changes (faster refresh window)
• auto-enable Widget Music taskbar deskband right after registration so it does not disappear after updates/re-register

Key changes

• host protocol additions in shared/WidgetMusicProtocol.h
• safe int64 JSON parser in shared/Json.h
• timeline extraction and state emission in WidgetMusicHost/src/main.cpp
• deskband timeline parsing, progress timer, hover popup handling, and full-mode text behavior in WidgetMusicDeskband/src/Deskband.cpp
• new helper script scripts/Enable-WidgetMusicTaskbar.ps1
• registration flow now attempts auto-enable in scripts/Register-WidgetMusic.cmd

Validation

• scripts/Build.cmd Debug (success)
• scripts/Build.cmd for Release|x64 (success)
• scripts/Verify-WidgetMusicGoal.ps1 (passes)
• scripts/Inspect-WidgetMusicTaskbar.ps1 confirms WidgetMusicDeskbandWindow visible on taskbar after enable path