feat(terminal): replace ghostty-web with an in-repo libghostty-vt adapter

The terminal ran on the ghostty-web npm package plus a hand-written patch,
and every rendering bug (recycled rows, duplicated reflow fragments, prompt
artifacts) had to be worked around from outside. The emulator now is the
official libghostty-vt C ABI compiled to WebAssembly, driven by a browser
adapter ported from T3 Code (MIT, notice in LICENSE-T3CODE) and owned in
packages/ui/src/lib/ghostty. The artifact is reproducible with
scripts/build-libghostty-wasm.sh, including a workaround for Zig 0.15.2 on
macOS 27 SDKs.

On top of the port: one WASM instance per page with every tab kept mounted
and hidden tabs paused; history replayed at the PTY size it was drawn for;
shells spawned only after the first fitted grid so zsh never prints the
PROMPT_SP marker; box drawing, block elements and Powerline arrows drawn
procedurally to the exact cell so TUI borders and block logos have no gaps
between rows; a software-rasterized canvas so Gecko renders every tab's text
with the same smoothing; the symbols-only Nerd Font bundled instead of a CDN
fetch; touch selection and scrolling driven through the surface API; a copy
button in the tab strip for touch hosts; localized aria labels.

Testing: bun tests run the real WASM (reflow, palette, replay isolation,
recycled rows, box glyph geometry); viewport and view tests use a surface
double; verified in Chromium and Zen (windowed and headless) for crisp text,
new tabs, panel reopen, resize and box glyph rendering; package type-check,
oxlint/eslint on new files, web build.

packages/ui/package.json

@@ -7,6 +7,7 @@
   "scripts": {
     "dev": "tsc --noEmit --watch",
     "build": "tsc --noEmit",
+    "build:ghostty-wasm": "bash scripts/build-libghostty-wasm.sh",
     "type-check": "tsc --noEmit",
     "lint": "eslint \"./src/**/*.{ts,tsx}\" --config ../../eslint.config.js",
     "test": "node ../../scripts/run-isolated-tests.mjs src"
@@ -61,7 +62,6 @@
     "express": "^5.1.0",
     "fflate": "^0.8.3",
     "fuse.js": "^7.1.0",
-    "ghostty-web": "0.4.0-next.20.g1858a59",
     "heic2any": "^0.0.4",
     "html-to-image": "^1.11.13",
     "http-proxy-middleware": "^3.0.5",