feat: show banner for bare mirror repositories

- Add isMirror prop to GitToolbar\n- Show warning banner when repo is a bare mirror\n- Explain that editing/committing/pulling/merging are unavailable\n- Suggest deleting and recreating to enable full features\n\nQuality gates: vitest (43 passed)

apps/web/src/components/git-toolbar.tsx

@@ -18,6 +18,7 @@ interface GitToolbarProps {
   currentBranch: string;
   branches: string[];
   hasRemote: boolean;
+  isMirror: boolean;
   onBranchChange: (branch: string) => void;
   onRefresh: () => void;
 }
@@ -28,6 +29,7 @@ export const GitToolbar = ({
   currentBranch,
   branches,
   hasRemote,
+  isMirror,
   onBranchChange,
   onRefresh,
 }: GitToolbarProps) => {
@@ -136,7 +138,13 @@ export const GitToolbar = ({
   return (
     <div className="git-toolbar">
       {error && <div className="toolbar-error">{error}</div>}
-      
+      {isMirror && (
+        <div className="warning-message">
+          <Icon name="warning" size="sm" /> This repository is a bare mirror.
+          Editing, committing, pulling, and merging are not available.
+          Delete and recreate it to enable full workspace features.
+        </div>
+      )}
       <div className="toolbar-row">
         <div className="toolbar-group">
           <select