Bot context window incomplete + queue tracks missing metadata

Several issues were identified during a music bot session:

### 1. Queue tracks missing title/artist metadata
The `get_queue` response returns `"Unknown title"` and `"Unknown artist"` for all tracks, including the currently playing one. Only the duration is populated. This makes it impossible for the bot to reason about what's in the queue or what's currently playing.

**Expected:** Each track in the queue should include its title and artist at minimum.

### 2. Conversation history not fully passed to bot context
The bot's context appears to be truncated — older messages from the same session are not included. This was observed when the bot could not see messages from earlier in the same conversation thread, despite them existing in the channel.

**Expected:** The full relevant conversation history (or at least a configurable scrollback window) should be passed as context on each invocation.

### 3. Referenced message context starts too late
Related to the above — when a user replies to a message, the bot's context seems to begin only from around that referenced message, rather than from the start of the session.

**Expected:** Context should ideally include the full session or be explicitly bounded in a predictable way.