feat(expressions): custom emojis and stickers per space

Emojis and stickers get separate tables on purpose: an emoji sits inside a
sentence and a sticker is the whole message, so their sizes, limits and render
paths differ.

Emoji names are unique per space and restricted to letters, digits and
underscore — :name: has to resolve to one image, and a space or colon inside
the name would make the reference impossible to delimit. Sticker names are
labels picked from a grid, so they accept anything.

Rendering reuses the existing markdown pipeline by rewriting :name: into image
syntax, which needs no plugin. Code spans and fences are left alone: text
someone wrapped in backticks was meant to be shown literally, and turning it
into an image would destroy what they wrote.

Messages carry stickerId with ON DELETE set null — removing a sticker from the
space must not delete the history of everyone who used it. The server refuses a
sticker from another space, which would otherwise leak images between unrelated
servers.

Expressions load once per space and stay in memory: the message renderer
consults the map for every :name: it finds, and a request per lookup would turn
each message into a cascade.

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

packages/web/src/components/layout/AppLayout.tsx

@@ -1,4 +1,5 @@
 import React, { useEffect } from 'react';
+import { useExpressionStore } from '../../stores/expressionStore';
 import { useParams, useNavigate } from 'react-router-dom';
 import { SpaceSidebar } from './SpaceSidebar';
 import { ChannelSidebar } from './ChannelSidebar';
@@ -217,6 +218,15 @@ export function AppLayout() {
   const setCurrentSpace = useSpaceStore((s) => s.setCurrentSpace);
   const loadSpaceDetail = useSpaceStore((s) => s.loadSpaceDetail);
   useSpotifyActivity();
+
+  // Emojis e figurinhas do espaço atual, carregados uma vez por espaço: o
+  // render de mensagem consulta o mapa a cada `:nome:`, e buscar por mensagem
+  // viraria uma cascata de requisições.
+  const expressionSpaceId = useSpaceStore((s) => s.currentSpaceId);
+  const loadExpressions = useExpressionStore((s) => s.load);
+  useEffect(() => {
+    if (expressionSpaceId) void loadExpressions(expressionSpaceId);
+  }, [expressionSpaceId, loadExpressions]);
   const setCurrentChannel = useChatStore((s) => s.setCurrentChannel);
   const loadMessages = useChatStore((s) => s.loadMessages);
   const setIsMobile = useUIStore((s) => s.setIsMobile);