fix(track): VS Code caret via the MSAA system caret; no tracking stall on a blocking app (#367)

[Maxaubert]

Closes #367. Stacked on #366 (which is stacked on #364).

1. VS Code caret.

• VS Code's editor is an EditContext element (native-edit-context). Its UIA caret and selection stay at the start of the line wherever the caret is, so Wind only followed line changes.
• A probe shows Chromium's MSAA system caret (OBJID_CARET) tracks it exactly:
  • End: x went from 261 to 556;
  • each character typed: +17 px.
• For that element class only, the MSAA caret on the same line wins (msaa-editcontext).
• Edge textareas are left alone: their UIA caret is right and their MSAA caret lags it by about 100 ms.
• The class is cached per focus and window. A stale cache once sent MSAA queries into Notepad; that is fixed here.

2. Tracking stalls.

• One app that does not answer a UIA call stalls all tracking.
• UIA calls are now capped at 500 ms.
• GetFocusedElement ignores that cap: it blocked for 3 s at Notepad's activation. It now runs on a Wind focus lookup thread:
  • the tracker waits at most 150 ms, then resolves without UIA;
  • no new lookup starts while one is stuck;
  • a late answer is reused if it is under 250 ms old and for the same window.
• With focus-following off, an app with a classic Win32 caret skips the lookup entirely; that caret already wins.
• Resolves over 200 ms log slow resolve with the phase.

Lookup thread verified (runs 28 to 32, 30 switches per app):

• 0 unfollowed switches, and 0 missed moves in Notepad and Edge.
• No stall over 1 s. Before, there was one 3 s stall about every 18 Notepad switches.
• Edge is now followed at the first keystroke (about 0.33 s after a switch). Before, a caret Edge moved by itself during activation was followed at 0.09 s.

Verified on the signed UIAccess build

• Scripted app switches, 6 per app per run, typing, Home and End right after each switch, with trackLog.

  App	Before	After (runs 20 to 22)
  VS Code	36 of 36 moves missed, 5 of 6 switches never followed	Every switch followed right after the first keystroke (0.73 to 0.8 s after the switch)
  Notepad		0 missed in 2 of 3 runs. One 3 s stall in 18 switches remains, at an activation with no Win32 caret yet.
  Edge		0 missed

• No stall over 1 s in runs 21 and 22.

• build.bat test: 572/572 pass.

Version 0.23.3.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KPUNAWcwghXdHCApcKKjSG