Add app update detection and multi-folder project support

Feature 1 - Update Detection: Query Gitea releases API on startup (3s
delay) and every 24h, compare patch versions by platform, show pulsing
"Update" button in TopBar with dialog for release notes/downloads.
Settings: auto-check toggle, manual check, dismiss per-version.

Feature 2 - Multi-Folder Projects: Replace single `path` with
`paths: Vec<ProjectPath>` (host_path + mount_name). Each folder mounts
to `/workspace/{mount_name}`. Auto-migrate old single-path JSON on load.
Container recreation via paths-fingerprint label. AddProjectDialog and
ProjectCard support add/remove/edit of multiple folders.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src/components/settings/UpdateDialog.tsx

@@ -0,0 +1,121 @@
+import { useEffect, useRef, useCallback } from "react";
+import { openUrl } from "@tauri-apps/plugin-opener";
+import type { UpdateInfo } from "../../lib/types";
+
+interface Props {
+  updateInfo: UpdateInfo;
+  currentVersion: string;
+  onDismiss: () => void;
+  onClose: () => void;
+}
+
+export default function UpdateDialog({
+  updateInfo,
+  currentVersion,
+  onDismiss,
+  onClose,
+}: Props) {
+  const overlayRef = useRef<HTMLDivElement>(null);
+
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === "Escape") onClose();
+    };
+    document.addEventListener("keydown", handleKeyDown);
+    return () => document.removeEventListener("keydown", handleKeyDown);
+  }, [onClose]);
+
+  const handleOverlayClick = useCallback(
+    (e: React.MouseEvent<HTMLDivElement>) => {
+      if (e.target === overlayRef.current) onClose();
+    },
+    [onClose],
+  );
+
+  const handleDownload = async (url: string) => {
+    try {
+      await openUrl(url);
+    } catch (e) {
+      console.error("Failed to open URL:", e);
+    }
+  };
+
+  const formatSize = (bytes: number) => {
+    if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(0)} KB`;
+    return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+  };
+
+  return (
+    <div
+      ref={overlayRef}
+      onClick={handleOverlayClick}
+      className="fixed inset-0 bg-black/50 flex items-center justify-center z-50"
+    >
+      <div className="bg-[var(--bg-secondary)] border border-[var(--border-color)] rounded-lg p-6 w-[28rem] max-h-[80vh] overflow-y-auto shadow-xl">
+        <h2 className="text-lg font-semibold mb-3">Update Available</h2>
+
+        <div className="flex items-center gap-2 mb-4 text-sm">
+          <span className="text-[var(--text-secondary)]">{currentVersion}</span>
+          <span className="text-[var(--text-secondary)]">&rarr;</span>
+          <span className="text-[var(--accent)] font-semibold">
+            {updateInfo.version}
+          </span>
+        </div>
+
+        {updateInfo.body && (
+          <div className="mb-4">
+            <h3 className="text-xs font-semibold uppercase text-[var(--text-secondary)] mb-1">
+              Release Notes
+            </h3>
+            <div className="text-xs text-[var(--text-primary)] whitespace-pre-wrap bg-[var(--bg-primary)] rounded p-3 max-h-48 overflow-y-auto border border-[var(--border-color)]">
+              {updateInfo.body}
+            </div>
+          </div>
+        )}
+
+        {updateInfo.assets.length > 0 && (
+          <div className="mb-4 space-y-1">
+            <h3 className="text-xs font-semibold uppercase text-[var(--text-secondary)] mb-1">
+              Downloads
+            </h3>
+            {updateInfo.assets.map((asset) => (
+              <button
+                key={asset.name}
+                onClick={() => handleDownload(asset.browser_download_url)}
+                className="w-full flex items-center justify-between px-3 py-2 text-xs bg-[var(--bg-primary)] border border-[var(--border-color)] rounded hover:border-[var(--accent)] transition-colors"
+              >
+                <span className="truncate">{asset.name}</span>
+                <span className="text-[var(--text-secondary)] ml-2 flex-shrink-0">
+                  {formatSize(asset.size)}
+                </span>
+              </button>
+            ))}
+          </div>
+        )}
+
+        <div className="flex items-center justify-between">
+          <button
+            onClick={() => handleDownload(updateInfo.release_url)}
+            className="text-xs text-[var(--accent)] hover:text-[var(--accent-hover)] transition-colors"
+          >
+            View on Gitea
+          </button>
+          <div className="flex gap-2">
+            <button
+              onClick={onDismiss}
+              className="px-3 py-1.5 text-xs text-[var(--text-secondary)] hover:text-[var(--text-primary)] transition-colors"
+            >
+              Dismiss
+            </button>
+            <button
+              onClick={onClose}
+              className="px-3 py-1.5 text-xs bg-[var(--bg-tertiary)] border border-[var(--border-color)] rounded hover:bg-[var(--border-color)] transition-colors"
+            >
+              Close
+            </button>
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+}