A catalog that can say a title is not yours

A store with paid titles had nothing to tell this client and no way for it to
listen: the catalog carried no price, no entitlement and no sign-in, so a gated
download could only come back 403 and leave the window guessing why.

The knowledge belongs on the server, not here. This client serves whichever
catalog a registry names, so anything it knew about a particular shop would be
a rule that breaks every other one. WarpEngine 0.5 answers GET /api/service with
what it offers and puts an `access` block on every entry; this reads both. There
is no store name anywhere in the diff.

- **0.5 is a dialect of its own**, the older shape with `access` added. The
  version list is exhaustive over the selector, so adding it was a compile error
  until somebody said what it reads like — which is what that switch is for.
- **A card shows a price and a Buy button** when a title is not yours, opening
  the store's own page. Buying stays in a browser: a checkout rebuilt here would
  be a second place to get card handling wrong.
- **Signing in is the device grant**: a short code, the person's own browser, and
  no password crossing this window. The token goes in the OS keychain through
  safeStorage — one per store — and where no keychain exists it is not stored at
  all rather than written out in the clear.
- **Owned / To buy** join the categories, since owning something is not the same
  as having installed it.

Three things worth stating about the shape:

The bearer token stops at the origin that issued it. A gated download redirects
to signed storage — often somebody else's host — and some object stores refuse a
request outright when an Authorization header arrives alongside the signature.

An absent access block is not "free". It is an engine too old to have an
opinion, and only one of those two is a reason to offer somebody a sign-in, so
the three states are kept apart all the way to the card.

state.json does not carry entitlement. Whether somebody may download a title is
the server's answer to a question asked now; a copy on disk would go stale on the
next purchase or refund, and a stale yes is the dangerous direction.

A store with no sign-in shows none, and every WarpEngine before 0.5 is such a
store: no Account block, no prices, no new categories. The smoke test against the
live catalog reports exactly that — `sign-in: not offered`, `access: open:13`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/renderer/index.html

@@ -36,6 +36,17 @@
         <button id="add-store" class="btn btn-ghost btn-wide"></button>
       </section>
 
+      <!--
+        Signing in, and who is signed in. The whole block is hidden where the catalog
+        offers no sign-in at all, which is most of them: a greyed-out button is telling
+        somebody about a door that does not exist.
+      -->
+      <section class="side-block" id="account-block" hidden>
+        <h2 class="side-head" id="head-account"></h2>
+        <p class="side-quiet-text" id="account-state"></p>
+        <button id="account-action" class="btn btn-ghost btn-wide"></button>
+      </section>
+
       <section class="side-block side-cats">
         <h2 class="side-head" id="head-cats"></h2>
         <nav class="cats" id="cats"></nav>
@@ -74,6 +85,22 @@
     </aside>
 
     <div class="content">
+      <!--
+        The code to type into a browser. A panel over the grid rather than a screen of
+        its own: the catalog is still there and still readable, and the sign-in is
+        something happening elsewhere that this window is only reporting on.
+      -->
+      <section id="signin" class="signin" hidden>
+        <h2 id="signin-title"></h2>
+        <p id="signin-body"></p>
+        <p class="signin-code" id="signin-code"></p>
+        <p class="signin-waiting" id="signin-waiting"></p>
+        <div class="signin-actions">
+          <button id="signin-open" class="btn btn-secondary"></button>
+          <button id="signin-cancel" class="btn btn-ghost"></button>
+        </div>
+      </section>
+
       <!-- Shown instead of the grid when there is nothing to drive yet. -->
       <section id="gate" class="gate" hidden>
         <h1 id="gate-title"></h1>