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

apps/desktop/AGENTS.md

@@ -61,7 +61,7 @@ bun typecheck              # TypeScript check
 From monorepo root, run `bun dist` to execute the full pipeline automatically (via Turbo task dependencies):
 
 1. **Build server**: `apps/server` → `vite build` → `.output/`
-2. **Compile server**: `apps/server` → `bun compile.ts` → `out/server-{platform}`
+2. **Compile server**: `apps/server` → `bun compile.ts` → `out/server-{os}-{arch}`
 3. **Package desktop**: `apps/desktop` → `electron-vite build` + `electron-builder` → distributable
 
 The `electron-builder.yml` `extraResources` config reads binaries directly from `../server/out/`, no manual copy needed.