shopping: ship as plugin, integrate phone view into relay UI, fix sync

Restructure the shopping-list feature end to end:

  - New public/plugins/shopping/ plugin with backend.php (proxy
    routes registered via PluginManager::onApiRoute), shopping.js
    (self-contained; injects the header Shopping button, owns the
    picker dialog + sync loop via hyprcrd.hooks), plugin.json and a
    placeholder css file. Core no longer knows about shopping —
    index.php loses the static button and the proxy block, app.js
    loses the initShopping wiring, the old js/modules/shopping.js
    is gone.
  - Phone view moves out of a standalone /shopping page and into
    the relay UI as a regular `view-shopping` behind a nav-burger
    entry (relay/ui/layout.php + app.js + style.css). Same session
    auth as compose/chat/account — no separate login. Auto-refresh
    every 4 s while the view is active; no manual refresh button.
    Headings "# h1 … ###### h6" render between items for grouping.
    Orphan section headings (no open items under them) are hidden.
  - Sync: drop timestamp cursors (broke across SQLite-UTC / PHP
    timezones and silently blocked pushes after a pull). Both sides
    diff the (uid, title, body) triple instead — timezone-agnostic
    and authoritative. Client ticks push-before-pull so fresh local
    edits land on the relay before a stale pull can overwrite them.
    Relay drops its "server newer" guard and stamps server times
    with gmdate so anything left comparing to SQLite is UTC.
  - Client also ticks on cards.reloaded, not just sync.tick, so
    any edit path (editor save, checkbox toggle, context menu,
    undo) pushes the update immediately.
  - Tests: updated for the plugin (still uses the same selectors
    because the plugin injects the same ids), plus a plugin-
    registration check and "(no active list)" option assertion.
  - Help section copy updated — references the Shopping header
    button and the shopping tab in the relay UI rather than the
    gone /shopping URL.

Both #einkauf and #shopping work as trigger tags; phone is
check-only, editing stays in hyprcrd. Version bumped to 1.9.21.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

relay/ui/layout.php

@@ -23,6 +23,7 @@ if (!defined('RELAY_BOOTSTRAPPED')) { http_response_code(404); exit; }
         <span id="nav-user" class="user"></span>
         <button id="nav-compose" class="nav-btn active" onclick="showView('compose')"><i class="ph ph-pencil-line"></i> compose</button>
         <button id="nav-chat" class="nav-btn" onclick="showView('chat')"><i class="ph ph-chat-circle-dots"></i> chat</button>
+        <button id="nav-shopping" class="nav-btn" onclick="showView('shopping')"><i class="ph ph-shopping-cart"></i> shopping</button>
         <button id="nav-account" class="nav-btn" onclick="showView('account')"><i class="ph ph-user-circle"></i> account</button>
         <button id="nav-admin" class="nav-btn hidden" onclick="showView('admin')"><i class="ph ph-users"></i> users</button>
         <button class="nav-btn danger" onclick="doLogout()"><i class="ph ph-sign-out"></i> logout</button>
@@ -210,6 +211,21 @@ if (!defined('RELAY_BOOTSTRAPPED')) { http_response_code(404); exit; }
     </div>
 </div>
 
+<!-- ── Shopping view ── -->
+<!-- Phone-friendly checklist. Shows only unchecked "- [ ]" items
+     from the currently active shopping card. Tapping an item flips
+     it to "- [x]" on the relay in place; hyprcrd pulls that back on
+     the next sync tick. Edits to item text stay in hyprcrd. -->
+<div id="view-shopping" class="hidden">
+    <div class="shopping-wrap">
+        <div class="shopping-top">
+            <span id="shopping-title" class="pixel" style="font-size:11px;color:var(--bright);">loading…</span>
+        </div>
+        <div id="shopping-err" class="shopping-err hidden"></div>
+        <ul id="shopping-items" class="shopping-items"></ul>
+    </div>
+</div>
+
 <!-- ── Chat view ── -->
 <div id="view-chat" class="hidden">
     <div class="chat-layout">