fix: 1.1.1.3 online installer 5.8M + mods toggle + ZGC vs G1GC conflict

- server/main.py BUILDS_DIR absolute + /launcher/download/online,offine-setup
- site index/js online->/download/online 5.8M
- LaunchCommandBuilder skip G1GC when systemBasedJvm (ZGC conflict -> Bootstrap crash)
- JFXLauncher toggle robust rename + FileAlreadyExists fix

server/main.py

@@ -43,7 +43,7 @@ logger = structlog.get_logger(__name__)
 # Cache for manifests - expires after 5 minutes
 manifest_cache = TTLCache(maxsize=100, ttl=300)
 
-BUILDS_DIR = Path("builds")
+BUILDS_DIR = Path(__file__).parent / "builds"
 VERSIONS_DIR = BUILDS_DIR / "versions"
 WHITELIST_DIR = Path(__file__).parent / "whitelist"
 
@@ -1813,6 +1813,43 @@ async def download_jre(request: Request):
             return await send_file_async(pp, request, content_type="application/zip", cache=True)
     raise HTTPException(404, "JRE zip not found on server")
 
+def _find_latest_setup(pattern: str) -> Path | None:
+    """Find latest Go setup exe by pattern (Online/Offline)"""
+    cands = list(BUILDS_DIR.glob(pattern))
+    if not cands:
+        return None
+    # sort by version key from filename
+    def ver_key(p: Path):
+        # ZernMC-Online-Setup-1.1.1.2.exe -> 1.1.1.2
+        name = p.stem
+        ver = name.split("-")[-1]
+        try:
+            return tuple(int(x) for x in ver.split("."))
+        except:
+            return (0,)
+    cands.sort(key=ver_key, reverse=True)
+    return cands[0]
+
+@app.get("/launcher/download/online")
+async def download_online_setup(request: Request):
+    """Download online Go installer (5.8M, STANDALONE EXE without bundled JRE)"""
+    p = _find_latest_setup("ZernMC-Online-Setup-*.exe")
+    if p and p.exists():
+        return await send_file_async(p, request, content_type="application/vnd.microsoft.portable-executable", cache=True)
+    raise HTTPException(404, "Online installer not found")
+
+@app.get("/launcher/download/offline-setup")
+async def download_offline_setup(request: Request):
+    """Download offline Go installer (STANDALONE EXE with embedded build, ~100M)"""
+    p = _find_latest_setup("ZernMC-Offline-Setup-*.exe")
+    if p and p.exists():
+        return await send_file_async(p, request, content_type="application/vnd.microsoft.portable-executable", cache=True)
+    # fallback: try legacy offline zip embed name without -Setup
+    p2 = _find_latest_setup("ZernMC-Offline-*.exe")
+    if p2 and p2.exists():
+        return await send_file_async(p2, request, content_type="application/vnd.microsoft.portable-executable", cache=True)
+    raise HTTPException(404, "Offline installer not found")
+
 @app.get("/launcher/download/zip/{filename}")
 async def download_launcher_zip(filename: str, request: Request = None):
     """Download specific launcher ZIP archive"""