Revert cosmetic GUI reformatting; keep only the shared-loader change

The previous commit's deno-fmt pass rewrote the already-merged GUI files
(gui/app.html, gui/app.js, gui/server.js) wholesale, which SonarCloud then
counted as "new code" — and app.js's kind/strata constants duplicated the new
CLI/test, leaving duplication at 4.4% (> 3%).

Restore gui/app.html and gui/app.js to their merged (main) state, and keep
only the functional shared-loader change in gui/server.js and
scripts/validate-cartridges.js (route both through src/cartridges.js so the
cartridge walk lives in exactly one place). Narrow deno.json fmt.include to the
files this PR actually authors, so the merged GUI shell is no longer reformatted.

Verified (Deno 2.8.3): deno fmt --check, deno lint, deno task test (59/59),
deno task build (1/1), GUI /api/cartridges live probe — all green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A1BaAhqxUjkgVb1yg1sZap

Author: claude

deno.json

@@ -20,7 +20,7 @@
     "semiColons": false,
     "singleQuote": false,
     "proseWrap": "preserve",
-    "include": ["bin/", "gui/", "scripts/", "src/cartridges.js", "test/run_all.js", "deno.json"]
+    "include": ["bin/", "src/cartridges.js", "test/run_all.js", "deno.json"]
   },
   "lint": {
     "rules": {