refactor: convert frontend from submodule to true monorepo

Convert frontend from Git submodule to a regular monorepo directory for simplified development workflow.

Changes:
- Remove frontend submodule tracking (mode 160000 gitlink)
- Add all frontend source files directly to main repository
- Remove frontend/.git directory
- Update CLAUDE.md to clarify true monorepo structure
- Update Frontend Architecture documentation (React Router v6, Socket.IO, Leaflet, ErrorBoundary)

Benefits of Monorepo:
- Single git clone for entire project
- Unified commit history
- Simpler CI/CD pipeline
- Easier for new developers
- No submodule sync issues
- Atomic commits across frontend and backend

Frontend Files Added:
- All React components (MapView, ErrorBoundary, TaskList, SocialFeed, etc.)
- Context providers (AuthContext, SocketContext)
- Complete test suite with MSW
- Dependencies and configuration files

Branch Cleanup:
- Using 'main' as default branch (develop deleted)
- Frontend no longer has separate Git history

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/components/ErrorBoundary.js

@@ -0,0 +1,62 @@
+import React from "react";
+
+class ErrorBoundary extends React.Component {
+  constructor(props) {
+    super(props);
+    this.state = { hasError: false, error: null, errorInfo: null };
+  }
+
+  static getDerivedStateFromError(error) {
+    return { hasError: true };
+  }
+
+  componentDidCatch(error, errorInfo) {
+    console.error("ErrorBoundary caught an error:", error, errorInfo);
+    this.setState({
+      error: error,
+      errorInfo: errorInfo,
+    });
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div className="container mt-5">
+          <div className="alert alert-danger" role="alert">
+            <h2 className="alert-heading">Something went wrong</h2>
+            <p>
+              We're sorry, but something unexpected happened. Please try
+              refreshing the page.
+            </p>
+            {process.env.NODE_ENV === "development" && this.state.error && (
+              <details className="mt-3" style={{ whiteSpace: "pre-wrap" }}>
+                <summary>Error details (development only)</summary>
+                <p className="mt-2">
+                  <strong>Error:</strong> {this.state.error.toString()}
+                </p>
+                {this.state.errorInfo && (
+                  <p>
+                    <strong>Stack trace:</strong>
+                    <br />
+                    {this.state.errorInfo.componentStack}
+                  </p>
+                )}
+              </details>
+            )}
+            <hr />
+            <button
+              className="btn btn-primary"
+              onClick={() => window.location.reload()}
+            >
+              Refresh Page
+            </button>
+          </div>
+        </div>
+      );
+    }
+
+    return this.props.children;
+  }
+}
+
+export default ErrorBoundary;