fix(terminal): update ghostty-web to a build that clears recycled rows

ghostty-web 0.4.0 hands rows that scroll into view out of recycled WASM
page memory without clearing them, so after a tab or project switch the
new emulator showed the previous terminal's text (upstream #138). The fix
landed only in prereleases, so pin 0.4.0-next.20 and carry the local
block-glyph rendering patch over to the new dist file.

Verified in a production build: creating an emulator after disposing a
full one no longer exposes its rows, and switching between two projects
with live output in each keeps every terminal's content to itself.

packages/ui/package.json

@@ -61,7 +61,7 @@
     "express": "^5.1.0",
     "fflate": "^0.8.3",
     "fuse.js": "^7.1.0",
-    "ghostty-web": "^0.4.0",
+    "ghostty-web": "0.4.0-next.20.g1858a59",
     "heic2any": "^0.0.4",
     "html-to-image": "^1.11.13",
     "http-proxy-middleware": "^3.0.5",