Add user password change functionality

Introduced a backend API endpoint for changing user passwords with validation. Added a new "User Settings" page in the frontend to allow users to update their passwords, including a matching UI update for navigation and styles.

frontend/src/pages/UserSettingsPage.jsx

@@ -0,0 +1,100 @@
+import React, { useState } from "react";
+import { apiFetch } from "../api";
+import { useAuth } from "../state";
+
+export function UserSettingsPage() {
+  const { tokens, refresh } = useAuth();
+  const [form, setForm] = useState({
+    current_password: "",
+    new_password: "",
+    confirm_password: "",
+  });
+  const [message, setMessage] = useState("");
+  const [error, setError] = useState("");
+  const [busy, setBusy] = useState(false);
+
+  const submit = async (e) => {
+    e.preventDefault();
+    setMessage("");
+    setError("");
+    if (form.new_password.length < 8) {
+      setError("New password must be at least 8 characters.");
+      return;
+    }
+    if (form.new_password !== form.confirm_password) {
+      setError("Password confirmation does not match.");
+      return;
+    }
+
+    try {
+      setBusy(true);
+      await apiFetch(
+        "/me/password",
+        {
+          method: "POST",
+          body: JSON.stringify({
+            current_password: form.current_password,
+            new_password: form.new_password,
+          }),
+        },
+        tokens,
+        refresh
+      );
+      setForm({ current_password: "", new_password: "", confirm_password: "" });
+      setMessage("Password changed successfully.");
+    } catch (e) {
+      setError(String(e.message || e));
+    } finally {
+      setBusy(false);
+    }
+  };
+
+  return (
+    <div className="user-settings-page">
+      <h2>User Settings</h2>
+      <p className="muted">Manage your personal account security settings.</p>
+      {error && <div className="card error">{error}</div>}
+      {message && <div className="test-connection-result ok">{message}</div>}
+
+      <div className="card user-settings-card">
+        <h3>Change Password</h3>
+        <form className="grid two" onSubmit={submit}>
+          <div className="admin-field field-full">
+            <label>Current password</label>
+            <input
+              type="password"
+              value={form.current_password}
+              onChange={(e) => setForm({ ...form, current_password: e.target.value })}
+              required
+            />
+          </div>
+          <div className="admin-field">
+            <label>New password</label>
+            <input
+              type="password"
+              value={form.new_password}
+              onChange={(e) => setForm({ ...form, new_password: e.target.value })}
+              minLength={8}
+              required
+            />
+          </div>
+          <div className="admin-field">
+            <label>Confirm new password</label>
+            <input
+              type="password"
+              value={form.confirm_password}
+              onChange={(e) => setForm({ ...form, confirm_password: e.target.value })}
+              minLength={8}
+              required
+            />
+          </div>
+          <div className="form-actions field-full">
+            <button className="primary-btn" type="submit" disabled={busy}>
+              {busy ? "Saving..." : "Update Password"}
+            </button>
+          </div>
+        </form>
+      </div>
+    </div>
+  );
+}