Add user authentication with login/register

- Add users and sessions tables to database schema
- Add bcryptjs for password hashing
- Create auth API routes (login, register, logout, me)
- Add AuthProvider context for client-side auth state
- Update all API routes to require authentication and filter by userId
- Create login and register pages
- Add AppShell component for authenticated layout
- Update all pages to use AppShell and show user info
- Each user now has their own private entries and tags

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/AuthProvider.tsx

@@ -0,0 +1,88 @@
+"use client";
+
+import { createContext, useContext, useState, useEffect, useCallback } from "react";
+import { useRouter, usePathname } from "next/navigation";
+
+interface User {
+  id: string;
+  email: string;
+  name: string | null;
+}
+
+interface AuthContextType {
+  user: User | null;
+  isLoading: boolean;
+  logout: () => Promise<void>;
+  refresh: () => Promise<void>;
+}
+
+const AuthContext = createContext<AuthContextType>({
+  user: null,
+  isLoading: true,
+  logout: async () => {},
+  refresh: async () => {},
+});
+
+export function useAuth() {
+  return useContext(AuthContext);
+}
+
+const PUBLIC_PATHS = ["/login", "/register"];
+
+export function AuthProvider({ children }: { children: React.ReactNode }) {
+  const [user, setUser] = useState<User | null>(null);
+  const [isLoading, setIsLoading] = useState(true);
+  const router = useRouter();
+  const pathname = usePathname();
+
+  const fetchUser = useCallback(async () => {
+    try {
+      const res = await fetch("/api/auth/me");
+      const data = await res.json();
+      setUser(data.user);
+      return data.user;
+    } catch {
+      setUser(null);
+      return null;
+    } finally {
+      setIsLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    fetchUser().then((user) => {
+      if (!user && !PUBLIC_PATHS.includes(pathname)) {
+        router.push("/login");
+      }
+    });
+  }, [fetchUser, pathname, router]);
+
+  const logout = async () => {
+    try {
+      await fetch("/api/auth/logout", { method: "POST" });
+      setUser(null);
+      router.push("/login");
+    } catch {
+      // Ignore errors
+    }
+  };
+
+  const refresh = async () => {
+    await fetchUser();
+  };
+
+  // Show nothing while checking auth on protected pages
+  if (isLoading && !PUBLIC_PATHS.includes(pathname)) {
+    return (
+      <div className="min-h-screen flex items-center justify-center">
+        <div className="animate-pulse text-muted">Loading...</div>
+      </div>
+    );
+  }
+
+  return (
+    <AuthContext.Provider value={{ user, isLoading, logout, refresh }}>
+      {children}
+    </AuthContext.Provider>
+  );
+}