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/utils/customEmoji.test.ts

@@ -0,0 +1,44 @@
+import { describe, it, expect } from 'vitest';
+import { renderCustomEmojis, isCustomEmojiAlt } from './customEmoji';
+import type { SpaceEmoji } from '../api/client';
+
+const emoji = (name: string): SpaceEmoji => ({
+  id: '1', spaceId: 's', name, filename: `${name}.png`, uploaderId: null, createdAt: 0,
+});
+const lookup = (n: string) => (n === 'trollface' ? emoji('trollface') : undefined);
+const urlOf = (f: string) => `/api/uploads/${f}`;
+
+describe('renderCustomEmojis', () => {
+  it('troca um emoji conhecido por imagem', () => {
+    expect(renderCustomEmojis('olha :trollface: isso', lookup, urlOf))
+      .toBe('olha ![:trollface:](/api/uploads/trollface.png) isso');
+  });
+
+  it('deixa nome desconhecido como texto', () => {
+    expect(renderCustomEmojis('nada :inexistente: aqui', lookup, urlOf))
+      .toBe('nada :inexistente: aqui');
+  });
+
+  it('não mexe em código em linha', () => {
+    // Quem escreveu entre crases quis mostrar o texto literal.
+    expect(renderCustomEmojis('use `:trollface:` assim', lookup, urlOf))
+      .toBe('use `:trollface:` assim');
+  });
+
+  it('não mexe em bloco de código', () => {
+    const src = '```\n:trollface:\n```';
+    expect(renderCustomEmojis(src, lookup, urlOf)).toBe(src);
+  });
+
+  it('devolve o texto intacto quando não há dois-pontos', () => {
+    expect(renderCustomEmojis('sem nada', lookup, urlOf)).toBe('sem nada');
+  });
+});
+
+describe('isCustomEmojiAlt', () => {
+  it('reconhece o alt de emoji e ignora imagem comum', () => {
+    expect(isCustomEmojiAlt(':trollface:')).toBe(true);
+    expect(isCustomEmojiAlt('foto de praia')).toBe(false);
+    expect(isCustomEmojiAlt(undefined)).toBe(false);
+  });
+});