sync-event toasts, image pull ordering, stale banner field diff

- replace chat-bot sync notifications with a dedicated relay_sync_events
  queue: POST/GET /api/sync-events, drained by /api/relay/poll and
  surfaced as stacking toasts via caldav.js. Old /api/chat/bot removed,
  bot=1 rows purged on bootstrap, orange bot rendering dropped from
  relay UI. Chat thread stays clean.
- collab pull: fetch attachments BEFORE applying the body so the moment
  state.cards reflects the new reference the file is on disk. Fixes the
  "preview shows broken/missing image, editor shows it" race where the
  browser cached the 404 between attachment landing and user re-render.
- detail stale banner now compares title/body/color/tags in addition to
  updated_at — robust against second-granularity timestamp collisions
  and any other case where updated_at doesn't tick but content differs.

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

relay/inc/bootstrap.php

@@ -189,14 +189,31 @@ $chatColNames = array_column($chatCols, 'name');
 if (!in_array('seen', $chatColNames)) {
     $db->exec('ALTER TABLE chat_messages ADD COLUMN seen INTEGER NOT NULL DEFAULT 0');
 }
-// Bot notifications: automated sync confirmations ("alice synced: My Card").
-// `bot` column = 1 means the UI renders it as a system notification in the
-// orange accent color instead of a regular chat bubble.
-if (!in_array('bot', $chatColNames)) {
-    $db->exec('ALTER TABLE chat_messages ADD COLUMN bot INTEGER NOT NULL DEFAULT 0');
+// Sync-notification cleanup: the bot=1 chat messages turned out to clutter
+// the chat thread. The feature moved to its own `relay_sync_events` queue
+// (see below). Drop any leftover bot rows so they stop showing up in
+// users' threads. The `bot` column stays on disk (SQLite ALTER DROP needs
+// a full table rebuild — not worth it for an ignored nullable column).
+if (in_array('bot', $chatColNames)) {
+    $db->exec('DELETE FROM chat_messages WHERE bot = 1');
 }
 $db->exec('CREATE INDEX IF NOT EXISTS idx_chat_sender_state ON chat_messages(sender_id, id)');
 
+// Sync-event notifications: replaces the old bot-chat mechanism. When a
+// client syncs a card they received, they POST here; the sender polls
+// GET /api/sync-events and surfaces each as a transient toast. Rows are
+// short-lived — we drop fetched ones after an hour, unfetched after a day.
+$db->exec('CREATE TABLE IF NOT EXISTS relay_sync_events (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    recipient_id INTEGER NOT NULL,
+    sender_username TEXT NOT NULL,
+    body TEXT NOT NULL,
+    fetched INTEGER NOT NULL DEFAULT 0,
+    created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (recipient_id) REFERENCES tenants(id) ON DELETE CASCADE
+)');
+$db->exec('CREATE INDEX IF NOT EXISTS idx_sync_events_recipient ON relay_sync_events(recipient_id, id)');
+
 // Collaborative buckets: shared among multiple tenants. Each bucket has one
 // owner and a membership set. Buckets persist (not ephemeral) since they are
 // the container for ongoing collaboration — cleanup only when deleted.
@@ -300,6 +317,10 @@ $db->exec("DELETE FROM messages WHERE created_at < datetime('now', '-24 hours')"
 $db->exec("DELETE FROM attachments WHERE created_at < datetime('now', '-24 hours')");
 // Chat: 7 days, longer than card sync but still ephemeral
 $db->exec("DELETE FROM chat_messages WHERE created_at < datetime('now', '-7 days')");
+// Sync events are transient toasts — drop fetched ones after an hour,
+// everything after 24h regardless (sender was offline too long to care).
+$db->exec("DELETE FROM relay_sync_events WHERE fetched = 1 AND created_at < datetime('now', '-1 hour')");
+$db->exec("DELETE FROM relay_sync_events WHERE created_at < datetime('now', '-24 hours')");
 // Collab-card tombstones: 7 days so late pollers still see the delete.
 $db->exec("DELETE FROM collab_cards WHERE deleted = 1 AND updated_at < datetime('now', '-7 days')");
 // Collab-card locks: drop everything past its TTL on every request.