Fix Windows terminal rendering and ownership

[coneilen]

Summary

Fix the two Windows preview blockers that made terminal output unreadable and allowed Stop to target a different zmx session from the daemon-owned workspace session.

Changes

• Publish Winghostty v2 glyph snapshots with complete UTF-8 clusters, wide-cell occupancy, resolved colors, and independent accessibility text instead of the v1 pseudo-glyph cell path.
• Use Ghostty VT by default while retaining GRAPHCODE_EXPERIMENTAL_TERMINAL_VT=0 as the explicit legacy rollback.
• Stage VT cells and glyph data atomically so allocation or validation failures cannot partially replace the live terminal buffer.
• Canonicalize attach, resize, and teardown identities as graphcode-UUID exactly once.
• Register the shared zmx identity tests and document the renderer behavior, rollback, decoration limits, and live-pixel evidence boundary.

Test plan

RED: GRAPHCODE_ZIG0152 test src\TerminalSurface.zig --test-filter "real glyph snapshots" -> 1/1 executed; expected .snapshot, found .cells
GREEN: GRAPHCODE_ZIG0152 test src\TerminalSurface.zig --test-filter "real glyph snapshots" -> 1/1 passed
REGRESSION: Tools\windows\validate.ps1 -Task windows-shell -SkipTrayLive -ShellPart unit -ShellValidationRoot C:\g -> 747/747 passed; 54/54 sections executed

• Attach/resize identity RED: 1/1 executed; expected graphcode-session-a, found session-a.
• Teardown identity RED: 1/1 executed; expected graphcode-alpha-id, found alpha-id.
• Both focused identity GREEN runs passed 1/1.
• Final TerminalSurface.zig root passed 140/140.
• The complete configured Windows-shell gate passed before the final atomic-staging hardening, including smoke/stress, daemon roundtrip, tray contracts, concurrent handoff, and native UI Automation. The finalized code then passed the 140/140 focused root and 747/747 aggregate unit gate.
• No privacy-safe live terminal fixture was available for direct pixel-readability inspection; the tests establish the v2 payload and provider GDI path rather than human-observed candidate pixels.

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