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

turbo.json

@@ -9,6 +9,15 @@
     "compile": {
       "dependsOn": ["build"]
     },
+    "compile:linux": {
+      "dependsOn": ["build"]
+    },
+    "compile:mac": {
+      "dependsOn": ["build"]
+    },
+    "compile:win": {
+      "dependsOn": ["build"]
+    },
     "dist": {},
     "dist:linux": {},
     "dist:mac": {},
@@ -17,13 +26,13 @@
       "dependsOn": ["@furtherverse/server#compile"]
     },
     "@furtherverse/desktop#dist:linux": {
-      "dependsOn": ["@furtherverse/server#compile"]
+      "dependsOn": ["@furtherverse/server#compile:linux"]
     },
     "@furtherverse/desktop#dist:mac": {
-      "dependsOn": ["@furtherverse/server#compile"]
+      "dependsOn": ["@furtherverse/server#compile:mac"]
     },
     "@furtherverse/desktop#dist:win": {
-      "dependsOn": ["@furtherverse/server#compile"]
+      "dependsOn": ["@furtherverse/server#compile:win"]
     },
     "dev": {
       "cache": false,