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>

public/plugins/chat/chat.css

@@ -170,6 +170,9 @@
     white-space: pre-wrap;
     line-height: 1.4;
     border: 1px solid var(--t-border);
+    /* Pick up the user's card-radius design token so chat bubbles look
+       consistent with the rest of the surface (sharp / rounded / pill). */
+    border-radius: var(--ui-radius-card, 0px);
 }
 
 .chat-bubble.in {
@@ -192,11 +195,25 @@
     color: var(--t-dim);
     margin-top: 2px;
     font-family: var(--t-font-pixel);
+    display: flex;
+    align-items: center;
+    gap: 4px;
 }
 
 .chat-bubble.out + .chat-bubble-time { align-self: flex-end; }
 .chat-bubble.in + .chat-bubble-time { align-self: flex-start; }
 
+/* Read receipts: clock = sent (relay not yet acked), single check =
+   delivered (recipient polled), double check = seen (recipient opened
+   the thread). Single/double share the same icon size as the timestamp. */
+.chat-receipt {
+    font-size: 11px;
+    line-height: 1;
+}
+.chat-receipt.pending   { color: var(--t-dim); }
+.chat-receipt.delivered { color: var(--t-muted); }
+.chat-receipt.seen      { color: var(--t-accent); }
+
 #chat-thread-form {
     display: flex;
     align-items: center;