feat: /topic lists known topics + shared memory clarification

[royosherove]

Enhances /topic to show all known topics from memory-state dir. Fixes underscore encoding in display. Memory (MEMORY.md, daily notes) is shared across all topics.

[chatgpt-codex-connector]

💡 Codex Review

roundhouse/src/gateway/topic-command.ts

Lines 101 to 105 in b9a9eee

	setActiveTopic(chatId, topicName);
	const display = topicName === "main" || topicName === "off" ? "main (default)" : topicName;
	const isNew = topicName !== "main" && topicName !== "off";
	const emoji = isNew ? "📂" : "🏠";
	await postWithFallback(thread, `${emoji} Switched to topic: \`${display}\`\n\nAgent context is now independent for this topic.`);

Reject /topic outside private threads

handleTopic always stores the requested topic and confirms success, but topic routing is only applied when agentThreadId === "main" in applyTopicOverride (same file), so group/supergroup threads never actually switch context. In a group, /topic deploy currently replies “Switched to topic” even though subsequent messages still route to group:<chatId>; this is a behavior regression that can mislead users and break workflows that rely on topic isolation.

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