fix: address critical and major PR review issues

- Lazy-load Recharts via SparklineChart component with React.lazy + Suspense
- Gate mock auth fallback behind VITE_MOCK_AUTH env var in Login and Register
- Add ProtectedRoute component to guard authenticated routes
- Fix touch target size on New Alert button (min-h-10 -> min-h-12)
- Replace invalid safe-area-pb class with pb-[env(safe-area-inset-bottom)]
- Fix theme toggle button touch targets (min-h-10 -> min-h-12)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/pages/Register.tsx

@@ -33,10 +33,14 @@ export function Register() {
       const res = await api.post<{ user: User; token: string }>('/auth/register', { name, email, password })
       setAuth(res.user, res.token)
       navigate('/')
-    } catch {
-      // Fallback to mock auth for demo
-      setAuth({ ...mockUser, name, email }, 'mock-jwt-token')
-      navigate('/')
+    } catch (err) {
+      if (import.meta.env.VITE_MOCK_AUTH === 'true') {
+        // Fallback to mock auth for demo
+        setAuth({ ...mockUser, name, email }, 'mock-jwt-token')
+        navigate('/')
+      } else {
+        setError('Registration failed. Please try again.')
+      }
     } finally {
       setLoading(false)
     }