feat(discord): Implement /leave and /threads slash commands for better thread management

[pro5251]

Description

Implement two new Discord slash commands to enhance user control over bot presence and session lifecycle:

1. /leave [target]

   • Function: Instructs the bot to leave a thread.
   • Parameters: An optional target parameter (Channel picker) to specify a different thread. If omitted, the bot leaves the current thread.
   • Background Logic: Upon leaving, the bot should also clear its internal BotTurnTracker and session metadata for that specific thread to
     ensure a clean slate if it's reinvited later.

2. /threads

   • Function: Returns an ephemeral list of all active threads/sessions the bot is currently participating in within the current Server
     (Guild).
   • Benefit: Helps users discover where the bot is "working" and allows them to manage runaway sessions easily.

Use Case

• Case 1: Resetting a Conversation
  * User: "The bot is stuck in a loop or the context is too messy. I want it to start fresh."
  * Action: User types /leave in the thread. The bot exits. User then mentions the bot in the main channel to start a brand new, clean thread.

• Case 2: Remote Management
  * User: "I know the bot is active in a private thread somewhere, but I can't remember which one."
  * Action: User types /threads in any channel. The bot provides a list of links to active threads. User follows the link or uses /leave
  target:#thread-name to shut it down remotely.

• Case 3: Resource Optimization
  * Admin: "The bot is hitting its maximum session limit."
  * Action: Admin uses /threads to see idle or unnecessary active threads and uses /leave to free up session slots for other users.

Technical Notes

• Commands should be registered as Guild commands for immediate availability.
• Responses to these management commands should be ephemeral (only visible to the user) to avoid cluttering the chat.
• SessionPool needs a way to expose active keys filtered by the Discord platform and Guild ID.

Proposed Solution

No response