test(windows): run the Windows code under Wine; theme preview parity

Windows was previously only compile-checked. With Wine 11 (staging)
and mingw available, scripts/windows-wine-test.sh (`just
test-windows-wine`) builds expat/FreeType/fontconfig for mingw under
target/wine-deps and runs the test suites of ghostty-vt, unicode,
datastruct, input, os, config, terminal, crash, termio and cli under
Wine (~2,700 tests). New termio/tests/exec_windows.rs drives real
cmd.exe children over ConPTY through Termio (output, exit codes,
typing, 120 KiB writes, stop, start failure). Fixes found: Windows
paths from fs::canonicalize leaked the \\?\ prefix (new
ghostty_os::path::realpath strips it like Zig); ghostty-font compiles
hb-ft for bundled HarfBuzz on Windows; ~25 tests had Unix assumptions.
Wine limitations are ignored with reasons (ResizePseudoConsole stub,
no POSIX rename over existing files) - docs/rewrite/notes/windows-wine.md.

+list-themes preview parity (former KNOWN_DIFFERENCES rows 5-9): the
search box ports vaxis TextInput (word navigation and editing bindings,
grapheme-wise editing), ASCII-only case folding, light initial colors
until terminal reports arrive (no COLORFGBG), and load errors end the
preview with exit 1; PTY tests compare with /usr/bin/ghostty.

Test Plan:
- just test-windows-wine
- cargo test -p ghostty-cli --test list_themes_pty
- cargo test --workspace --no-fail-fast (3601 passed)

README.md

@@ -14,7 +14,8 @@ All of Ghostty's Zig code is ported: the Linux GTK app (verified at runtime
 and pixel-identical to Ghostty 1.3.1), the `libghostty` and `libghostty-vt`
 C APIs (same headers/ABI), WASM, crash reporting, and the macOS
 (Metal/CoreText) and Windows (ConPTY) code paths. macOS and Windows are
-compile-checked on Linux (`just check-macos`, `just check-windows`) but have
+compile-checked on Linux (`just check-macos`, `just check-windows`); the
+Windows test suites also run under Wine (`just test-windows-wine`), macOS has
 not been run natively. The Swift macOS app is not part of the port; it is a
 client of the libghostty C API.
 
@@ -63,6 +64,8 @@ build (see `docs/rewrite/notes/perf-P1.md`).
   Ghostty's own Zig code (sets up Zig 0.15.2 under `target/`).
 - `just visual-parity` — pixel comparison against the installed Ghostty in a
   headless nested weston.
+- `just test-windows-wine` — runs the Windows test suites (incl. ConPTY /
+  `cmd.exe` end-to-end tests) under Wine with mingw-w64.
 - `just check-all` — native gate plus macOS/Windows/WASM checks.
 
 ## Documentation