feat(legal): public privacy policy, terms, and homepage for OAuth verification

Adds login-free /privacy and /terms pages (rendered outside the authenticated
tree via a pathname switch in main.tsx) carrying the Google API Services Limited
Use disclosure, YouTube ToS / Google Privacy links, and contact + data-deletion
info. The sign-in screen now describes the app and links to both, satisfying
Google's homepage + privacy-policy requirements for the OAuth consent screen.

frontend/src/components/legal/PrivacyPolicy.tsx

@@ -0,0 +1,111 @@
+import LegalLayout, { CONTACT_EMAIL, H2, LegalLink } from "./LegalLayout";
+
+export default function PrivacyPolicy() {
+  return (
+    <LegalLayout title="Privacy Policy">
+      <p>
+        Subfeed is a personal, non-commercial project operated by an individual in Hungary
+        ("we", "us"). It lets you view and organize your own YouTube subscriptions as a
+        filterable feed. This policy explains what data Subfeed accesses, how it is used, and
+        the choices you have. By using Subfeed you agree to this policy.
+      </p>
+
+      <H2>What we access</H2>
+      <p>Subfeed only accesses data you explicitly authorize, in two separate steps:</p>
+      <ul className="list-disc pl-5 space-y-1">
+        <li>
+          <span className="text-fg font-medium">Sign-in (always):</span> your basic Google
+          profile — name, email address, profile picture, and Google account identifier — used
+          solely to create and identify your account.
+        </li>
+        <li>
+          <span className="text-fg font-medium">YouTube read (optional, opt-in):</span> with the{" "}
+          <code className="text-xs">youtube.readonly</code> scope, your list of YouTube
+          subscriptions and the public metadata of those channels and their videos (titles,
+          thumbnails, durations, view counts, publish dates), used to build your feed.
+        </li>
+        <li>
+          <span className="text-fg font-medium">YouTube manage (optional, opt-in):</span> with
+          the <code className="text-xs">youtube</code> scope, the ability to unsubscribe from a
+          channel on YouTube — performed only when you click to do so.
+        </li>
+      </ul>
+      <p>
+        You can use Subfeed with sign-in alone, and grant or decline each YouTube permission
+        independently.
+      </p>
+
+      <H2>How we use it</H2>
+      <p>
+        Your data is used exclusively to provide Subfeed's features to you: building and
+        displaying your personalized subscription feed, and carrying out actions (such as
+        unsubscribing) that you initiate. We do not use it for advertising, profiling, or any
+        purpose unrelated to the app.
+      </p>
+
+      <H2>Limited Use disclosure</H2>
+      <p>
+        Subfeed's use and transfer of information received from Google APIs to any other app
+        will adhere to the{" "}
+        <LegalLink href="https://developers.google.com/terms/api-services-user-data-policy">
+          Google API Services User Data Policy
+        </LegalLink>
+        , including the Limited Use requirements. We do not sell your data, do not transfer it
+        to third parties (except as needed to operate the app, e.g. the hosting infrastructure
+        we control), and do not use it for advertising.
+      </p>
+
+      <H2>Storage &amp; security</H2>
+      <p>
+        Data is stored in a private PostgreSQL database on a server we control, accessible only
+        to the operator. Google OAuth refresh tokens are encrypted at rest. Access is restricted
+        to the emails explicitly invited to the app. No system is perfectly secure, but we take
+        reasonable measures to protect your data.
+      </p>
+
+      <H2>Retention &amp; deletion</H2>
+      <p>
+        We keep your data while your account is active. You can revoke Subfeed's access to your
+        Google data at any time at{" "}
+        <LegalLink href="https://myaccount.google.com/permissions">
+          myaccount.google.com/permissions
+        </LegalLink>
+        ; once revoked, the stored tokens can no longer be used. To have your account and
+        associated data deleted, email{" "}
+        <a href={`mailto:${CONTACT_EMAIL}`} className="text-accent hover:underline">
+          {CONTACT_EMAIL}
+        </a>
+        .
+      </p>
+
+      <H2>Cookies</H2>
+      <p>
+        Subfeed sets a single, signed session cookie to keep you logged in. It is not used for
+        tracking or advertising, and there are no third-party analytics cookies.
+      </p>
+
+      <H2>YouTube &amp; Google</H2>
+      <p>
+        Subfeed uses YouTube API Services. By using Subfeed you also agree to the{" "}
+        <LegalLink href="https://www.youtube.com/t/terms">YouTube Terms of Service</LegalLink>,
+        and your use of Google data is subject to the{" "}
+        <LegalLink href="https://policies.google.com/privacy">Google Privacy Policy</LegalLink>.
+      </p>
+
+      <H2>Changes</H2>
+      <p>
+        We may update this policy; material changes will be reflected by the "Last updated" date
+        above. Continued use after a change constitutes acceptance.
+      </p>
+
+      <H2>Contact</H2>
+      <p>
+        Questions about this policy or your data:{" "}
+        <a href={`mailto:${CONTACT_EMAIL}`} className="text-accent hover:underline">
+          {CONTACT_EMAIL}
+        </a>
+        .
+      </p>
+    </LegalLayout>
+  );
+}