Add 'Detect and Join Conversation' button to Web UI and CLI

- Added /autonomous/join-conversation API endpoint in api.py
- Added 'Detect and Join Conversation' button to Web UI under Autonomous Actions
- Added 'autonomous join-conversation' command to CLI tool (miku-cli.py)
- Updated miku_detect_and_join_conversation_for_server to support force=True parameter
- When force=True: skips time limit, activity checks, and random chance
- Force mode uses last 10 user messages regardless of age
- Manual triggers via Web UI/CLI now work even with old messages

bot/static/index.html

@@ -576,6 +576,7 @@
     <button onclick="triggerAutonomous('engage')">Engage Random User</button>
     <button onclick="triggerAutonomous('tweet')">Share Tweet</button>
         <button onclick="triggerAutonomous('reaction')">React to Message</button>
+        <button onclick="triggerAutonomous('join-conversation')">Detect and Join Conversation</button>
         <button onclick="toggleCustomPrompt()">Custom Prompt</button>
       </div>