Web client: replies, reactions, threads and spaces

- Replies: Reply on a message puts it above the composer; the reply
  quotes it (sender and first line), and the quote goes to the message.
  Sent without the quoted fallback (Matrix 1.13); the fallback in older
  replies is not shown.
- Reactions: the six quick ones of the Android app or any other emoji,
  chips under the message with counts, yours highlighted; a chip adds
  yours or takes it back.
- Threads: matrix-js-sdk's thread support is on. Reply in thread opens
  the thread beside the room with its own composer; the root shows
  "N replies" and the last reply; Threads in the header lists them.
  Receipts are per thread (MSC3771): the room is marked read with its
  read marker and a separate receipt for "main", since /read_markers'
  receipt has no thread_id and would read every thread. Unread counts
  per thread (MSC3773) and a dot on unread threads.
  Two SDK quirks worked around: the thread view creates the thread
  object when a thread starts here (else the first reply's remote echo
  is dropped until reload), and the reply count is re-read from the
  root's bundled count after replies arrive (the SDK can count one
  twice).
- Spaces: kept out of the room list; a picker narrows the list to a
  space's rooms and its subspaces'. A space's page (/hierarchy) lists
  its rooms with Open or Join; admins add existing rooms, create new
  ones in it and take rooms out. New space in the + menu and picker.
- The room composer moved into RoomComposer.vue, shared by the room
  and the thread pane. New thread and space icons in apps/ui.
- Dev server: the Rust crypto's .wasm was lost to vite's pre-bundling,
  so E2EE never started under `pnpm web:dev`; the package is now served
  as it is in dev.

Server: /versions lists v1.1 to v1.14. matrix-js-sdk checks for the
exact version a feature came in, and with only v1.13 and v1.14 it kept
threads, per-thread unread counts, recursive relations and intentional
mentions off.

Tested in the browser against a local server: replies, reactions,
threads (new and existing, in plain and encrypted rooms, receipts
checked on the server) and spaces.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/components/JoinRoomDialog.vue

@@ -20,7 +20,7 @@ const directory = ref<IPublicRoomsChunkRoom[]>()
 const directoryError = ref('')
 const search = ref('')
 
-const joined = computed(() => new Set(chat.rooms.map((r) => r.roomId)))
+const joined = computed(() => new Set([...chat.rooms, ...chat.spaces].map((r) => r.roomId)))
 
 async function loadDirectory() {
   directoryError.value = ''