chat: read receipts (delivered + seen) and persisted active bucket

Read receipts on chat messages — single check for delivered (recipient
polled), double check for seen (recipient opened the thread). Pending
state shows a clock until the relay acks the post.

Relay (relay/):
* bootstrap.php: ALTER TABLE chat_messages ADD COLUMN seen + a
  (sender_id, id) index for the sender-side state poll. Migration is
  idempotent via PRAGMA table_info.
* routes/chat.php: two new routes
  - GET  /api/chat/sent?since=N — returns the receipt state (id,
    recipient_id, fetched, seen, created_at) for messages the caller
    sent. No body — sender already has the plaintext locally.
  - POST /api/chat/seen { peer } — marks every message FROM peer TO
    caller as seen=1. Idempotent. Frontend calls this when opening
    a thread; sender's next /sent poll picks the new state up.

Plugin backend (public/plugins/chat/backend.php):
* schema migration: chat_messages gets `delivered` and `seen` columns
  (idempotent), only meaningful for direction='out'.
* /api/chat/send: stores the relay's autoincrement id as `relay_id`
  on the local outgoing row so the receipt poll can match against it.
* /api/chat/poll: after the normal incoming pull, also calls
  GET /api/chat/sent?since=last_sent_relay_id and updates local
  outgoing rows with delivered/seen via UPDATE WHERE relay_id. The
  cursor (last_sent_relay_id state value) only advances past rows
  whose state is final (seen=1); rows still in flight stay re-pollable.
  Response now carries `receipts: <count>` so the frontend can refresh
  the open thread when state changes without new incoming.
* /api/chat/read: after the local is_read=1 update, fires a POST to
  the relay's /api/chat/seen so the sender gets the double-check.
  Silent on failure — the user already saw the messages locally.
* /api/chat/messages: SELECT now includes delivered, seen.

Plugin frontend (public/plugins/chat/chat.js):
* renderThread() appends a receipt icon to outgoing bubbles:
  - seen=1                      → ph-checks (accent, double check)
  - delivered=1, seen=0         → ph-check  (muted, single check)
  - both 0                       → ph-clock  (dim, pending)
  Incoming messages get nothing.
* pollOnce() refreshes the open thread when receipts > 0 even with
  no new incoming, so the icons update in real time while the user
  is looking at the thread.

CSS (public/plugins/chat/chat.css):
* .chat-bubble-time becomes flex with gap so timestamp + receipt
  icon sit on one line.
* .chat-receipt.pending / .delivered / .seen color tiers.

board: persist active bucket across reloads

* state.js: state.activeBucket initializes from
  localStorage.getItem('hyprcrd-active-bucket') || 'all'. New
  setActiveBucket(value) helper writes through to localStorage; new
  ensureActiveBucketValid() helper falls back to 'all' if the
  persisted id no longer exists in state.buckets.
* buckets.js: loadBuckets() calls ensureActiveBucketValid() right
  after the API fetch and before renderBar(). All four production
  assignments (delete-keep, delete-all, popover entry click, regular
  tab click) replaced with setActiveBucket() so the persisted value
  stays in sync. Tests still mutate state.activeBucket directly so
  they don't touch localStorage.

chore: bump version to 0.9.6

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

relay/inc/bootstrap.php

@@ -180,6 +180,16 @@ $db->exec('CREATE TABLE IF NOT EXISTS chat_messages (
     FOREIGN KEY (sender_id) REFERENCES tenants(id) ON DELETE SET NULL
 )');
 $db->exec('CREATE INDEX IF NOT EXISTS idx_chat_recipient ON chat_messages(recipient_id, fetched, id)');
+// Read receipts: `fetched` (already present) is "delivered" — set when the
+// recipient polls /api/chat. `seen` is "seen" — set when the recipient
+// opens the thread with the sender via POST /api/chat/seen. The sender
+// learns both states by polling GET /api/chat/sent.
+$chatCols = $db->query('PRAGMA table_info(chat_messages)')->fetchAll();
+$chatColNames = array_column($chatCols, 'name');
+if (!in_array('seen', $chatColNames)) {
+    $db->exec('ALTER TABLE chat_messages ADD COLUMN seen INTEGER NOT NULL DEFAULT 0');
+}
+$db->exec('CREATE INDEX IF NOT EXISTS idx_chat_sender_state ON chat_messages(sender_id, id)');
 
 // Collaborative buckets: shared among multiple tenants. Each bucket has one
 // owner and a membership set. Buckets persist (not ephemeral) since they are