feat: polls with live voting via WebSocket

- /poll command opens creation modal (2-10 options)
- PollDisplay with vote bars, percentages, live WS updates
- Backend: polls/poll_options/poll_votes tables, Create/Get/Vote endpoints
- attachPolls enriches message list responses
- POLL_UPDATE broadcast on vote for real-time sync

web/src/lib/slashCommands.ts

@@ -34,6 +34,7 @@ export const SLASH_COMMANDS: SlashCommand[] = [
   { name: 'greet', description: 'Friendly wave hello', transform: (a) => a ? GREET + ' ' + a : GREET + ' Hello!' },
   { name: 'me', description: 'Send an action message', transform: (a, u) => '*' + u + ' ' + a + '*' },
   { name: 'spoiler', description: 'Hide text as a spoiler', transform: (a) => '||' + a + '||' },
+  { name: 'poll', description: 'Create a poll', transform: (a) => a },
 ];
 
 export function findCommand(name: string): SlashCommand | undefined {