Trace data inaccessible after starting new session in TUI

[anandgupta42]

Problem

When using the TUI, trace data from previous sessions becomes inaccessible when a new session starts. The /trace command only works with the current active session, and there's no way to browse or view previous trace history from within the TUI.

Traces are persisted to disk (~/.local/share/altimate-code/traces/), but the TUI provides no UI to access them after the session ends.

Reported in #225.

Expected Behavior

• Users should be able to browse and view previous trace sessions from the TUI
• /trace should gracefully handle the case when no active session exists
• A dedicated command should exist for viewing trace history

Solution

• Add /traces slash command with a DialogTraceList component showing trace history
• Modify /trace to fall back to trace history when no active session
• Add sidebar hint for /traces command