refactor: simplify compile.ts to single-target and add per-platform compile scripts

- Rewrite compile.ts from 112 to 66 lines: single target with auto-detect host, remove multi-target batch logic
- Add compile:linux/mac/win scripts to server, root, and turbo configs
- Wire desktop dist:* to depend on matching server compile:* (avoid unnecessary cross-platform compilation)
- Update AGENTS.md docs across root, server, and desktop

package.json

@@ -10,6 +10,9 @@
   "scripts": {
     "build": "turbo run build",
     "compile": "turbo run compile",
+    "compile:linux": "turbo run compile:linux",
+    "compile:mac": "turbo run compile:mac",
+    "compile:win": "turbo run compile:win",
     "dev": "turbo run dev",
     "dist": "turbo run dist",
     "dist:linux": "turbo run dist:linux",