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

internal/db/db.go

@@ -509,5 +509,30 @@ CREATE TABLE IF NOT EXISTS server_groups (
 );
 CREATE INDEX IF NOT EXISTS idx_server_groups_server ON server_groups(server_id);
 ALTER TABLE channels ADD COLUMN IF NOT EXISTS group_id UUID REFERENCES server_groups(id) ON DELETE SET NULL;
+
+CREATE TABLE IF NOT EXISTS polls (
+	id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+	message_id UUID NOT NULL REFERENCES messages(id) ON DELETE CASCADE,
+	question TEXT NOT NULL,
+	created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+CREATE INDEX IF NOT EXISTS idx_polls_message ON polls(message_id);
+
+CREATE TABLE IF NOT EXISTS poll_options (
+	id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+	poll_id UUID NOT NULL REFERENCES polls(id) ON DELETE CASCADE,
+	text TEXT NOT NULL,
+	position INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX IF NOT EXISTS idx_poll_options_poll ON poll_options(poll_id);
+
+CREATE TABLE IF NOT EXISTS poll_votes (
+	id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+	option_id UUID NOT NULL REFERENCES poll_options(id) ON DELETE CASCADE,
+	user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+	UNIQUE (option_id, user_id)
+);
+CREATE INDEX IF NOT EXISTS idx_poll_votes_option ON poll_votes(option_id);
 `