feat(web): real chat list + P2P conversation view against live Tinode data

Phase 2 core loop: chat list and single-chat conversation now read/write real
Tinode topic data end to end, replacing the earlier hardcoded placeholders.

- lib/tinode/topics.ts: per-topic pub-sub layered on connection.ts's pattern
  (Topic.onData/onInfo/etc are single-slot callbacks, claimed once and fanned
  out). Implements the old app's subscribe lifecycle: `me` subscribed once
  per session (metadata only), each contact gets a one-shot preview
  subscription (withLaterData(1), never left), opening a conversation
  leaves-then-resubscribes with a full history page (withData, not
  withLaterData -- a preview prefetch already nudging _maxSeq would make
  withLaterData return empty).
- lib/tinode/hooks.ts: useChatList()/useTopicMessages() via
  useSyncExternalStore, snapshots cached and only invalidated on real
  topic-change notifications (not recomputed every render).
- lib/tinode/send.ts: sendText/retryMessage via createMessage+publishDraft
  (optimistic local echo), not the simpler publish() -- matches the old
  app's approach. retryMessage flushes the failed local entry and rebuilds
  before republishing, per the old app's context-menu retry handler.
- lib/messages/{time,avatar,attachments,status,preview,dispatch,drafty}:
  formatting utilities. Avatar color hash ports the old app's Java-style
  string hash but with modulus 11 (this design's palette) not the old app's
  16. @mention renders flat accent blue per the new design, not the old
  app's per-user hash color -- a deliberate simplification. File-type icons
  (PDF/Word/Excel/PPT) are new-design-only; the old app buckets all
  documents identically. Date/time formatting is written fresh against the
  design spec (today+time combined, weekday tier) since the old app never
  combines a relative-date word with a time in one string.
- ChatListColumn, MessageBubble, ConversationView: real components replacing
  the placeholder chat list and "占位" conversation view.
- tinode-sdk.d.ts: expanded with the real Topic/MetaGetBuilder/Drafty
  surface needed above, verified against the installed SDK source
  (createMessage/publishDraft/messages/msgStatus/noteRead/flushMessage/
  Drafty.format's exact treeBottomUp contract, MESSAGE_STATUS_* statics).

Verified end to end against the real backend: used the still-functional old
app (a second account, ixp355087) to create a real friendship and exchange
messages with the new app's test account, confirming the new chat list and
conversation view correctly render pre-existing real data, sending a new
message shows the right optimistic-then-delivered status transition, and
the old app receives it live in return.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/avatar.ts

@@ -0,0 +1,32 @@
+/**
+ * Deterministic avatar background color per user/topic ID. Algorithm (Java-style String#hashCode,
+ * rolling `hash = hash*31 + charCode`) ported from the old app's `letterTileColorId` -- but the old
+ * app's palette had 16 colors (`% 16`) where this design's token palette (index.css's --color-avatar-1
+ * through -11) has 11, so the modulus is adjusted to match; the hash function itself is unchanged.
+ */
+function stringToColorHash(value: string): number {
+  let hash = 0;
+  for (let i = 0; i < value.length; i++) {
+    hash = (hash << 5) - hash + value.charCodeAt(i);
+    hash = hash & hash;
+  }
+  return hash;
+}
+
+const AVATAR_COLOR_COUNT = 11;
+
+/** 1-based index matching the --color-avatar-1..11 tokens in index.css. */
+export function avatarColorIndex(id: string): number {
+  return (Math.abs(stringToColorHash(id)) % AVATAR_COLOR_COUNT) + 1;
+}
+
+const AVATAR_BG_CLASSES = Array.from({ length: AVATAR_COLOR_COUNT }, (_, i) => `bg-avatar-${i + 1}`);
+
+export function avatarBgClass(id: string): string {
+  return AVATAR_BG_CLASSES[avatarColorIndex(id) - 1];
+}
+
+/** First character of a display name, matching the old app's letter-tile convention. */
+export function avatarLetter(name: string | undefined): string {
+  return (name || '').trim().slice(0, 1) || '?';
+}