[0.9.1] Mobile: fixed topbar, global hive, per-message chat reply/switcher, forum subtopics, square module grid

- Topbar: single fixed line [logo][Personal][Community][avatar] in one dark
  tone (#121212) with gold accents only; the hive hexagons scroll below it.
- Hive: Personal/Community filter the home hive from any page; opening a
  category shows its modules as a 2x2 grid of square buttons (a lone odd
  button is centered instead of left-aligned).
- Chats: per-message reply (?replyTo=), chat switcher strip and quote banner;
  the message rate limit is lifted on mobile.
- Forums: optional subtopics (?topic=) with threaded rendering.
- Bottombar: fixed Inbox - PM - Write - Search - Graphos - Peers.

src/models/forum_model.js

@@ -503,7 +503,8 @@ module.exports = ({ cooler, tribeCrypto, forumCrypto }) => {
           text: c.text,
           author: c.author,
           timestamp: m.value.timestamp,
-          parent: c.branch || null
+          parent: c.branch || null,
+          subtopic: c.subtopic || null
         }));
       for (let r of replies) {
         const { positives: rp, negatives: rn } = await aggregateVotes(ssbClient, r.key);