feat: build.ps1 produces Launcher.exe + portable layout

- build a lean onefile Launcher.exe from src/launcher.py (stdlib-only, no
  PySide6/Pillow) alongside the onedir app build
- release dir is now the portable layout: Launcher.exe + app\ (CMBot.exe +
  config + version.txt)
- emit two zips: CMBot-<ver>.zip (self-update payload = app\ contents, what
  manifest.url points to) and CMBot-<ver>-portable.zip (initial install)
- launcher: harden logging setup for --windowed builds / read-only roots

Actual PyInstaller build must run on Windows; script is syntax-verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/launcher.py

@@ -214,16 +214,27 @@ def main(argv=None):
     args = parser.parse_args(argv)
 
     root = Path(args.install_root) if args.install_root else _default_install_root()
-    logging.basicConfig(
-        level=logging.INFO,
-        format="%(asctime)s  %(message)s",
-        handlers=[
-            logging.StreamHandler(),
-            logging.FileHandler(str(root / "launcher.log"), encoding="utf-8"),
-        ],
-    )
+    _setup_logging(root)
     return run(root, no_launch=args.no_launch)
 
 
+def _setup_logging(root):
+    """Configure logging defensively for both console and --windowed builds.
+
+    A PyInstaller --windowed exe has no stdout/stderr (StreamHandler(None) would
+    fail), and a read-only install root makes the file handler fail. Add each
+    handler only when it can be created so the launcher never crashes on logging.
+    """
+    handlers = []
+    if sys.stderr is not None:
+        handlers.append(logging.StreamHandler())
+    try:
+        handlers.append(logging.FileHandler(str(root / "launcher.log"), encoding="utf-8"))
+    except OSError:
+        pass
+    logging.basicConfig(level=logging.INFO, format="%(asctime)s  %(message)s",
+                        handlers=handlers)
+
+
 if __name__ == "__main__":
     sys.exit(main())