fix(shopping): stale-row cleanup, cache-busting, view persistence

Root cause of the doubled lists: the relay DB had stale rows from
previous activations that were never deleted. The composite PK
prevented same-uid duplicates but not leftover rows from cards that
were deactivated without a successful DELETE.

Fixes:
  - Client tick sends DELETE { keep: [active uids] } after every
    push cycle. The relay drops all rows for this tenant that aren't
    in the keep list — cleans up migration leftovers, failed deletes,
    old single-list sentinels, everything in one shot.
  - Relay DELETE endpoint accepts { keep: [...] } for bulk cleanup
    alongside the existing { card_uid } single-delete.
  - Relay layout.php adds cache-busting query strings on style.css
    and app.js via filemtime() so phone browsers pick up new code
    on deploy instead of serving stale cached versions.
  - showView persists the active view name to localStorage; after
    login the relay restores it instead of always landing on compose.
  - Shopping-list-box border/background removed — items have their
    own chrome, the box is just a flex grouper now.
  - View title is always "Shopping"; each list box keeps its own
    header with the card title. No more doubled name.

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

relay/ui/style.css

@@ -271,18 +271,14 @@ label.checkbox input[type="checkbox"] { accent-color:var(--accent); cursor:point
 .shopping-items .empty { list-style: none; text-align: center; padding: 40px 16px; color: var(--dim); background: transparent; border: none; cursor: default; }
 .shopping-items .empty:active { transform: none; }
 
-/* Multi-list stacked boxes */
+/* Multi-list stacked boxes — no own border/background so items
+   don't look doubled. The header provides section separation. */
 .shopping-list-box {
     list-style: none;
-    background: var(--surface);
-    border: 1px solid var(--border);
-    border-radius: var(--radius-lg);
-    padding: 10px;
     display: flex;
     flex-direction: column;
     gap: 6px;
 }
-.shopping-list-box:active { transform: none; }
 .shopping-list-header {
     font-weight: 600;
     font-size: 13px;