Rename session info endpoint from /sessions/:id/info to /sessions/:id/status
and update frontend tab label accordingly. Add /status slash command that
displays current session metrics (message count, context usage, cache hit
rate, used skills) as formatted text in any channel.
Add GET /bots/:bot_id/sessions/:session_id/info API endpoint that returns
per-session message count, latest input token usage with model context window,
aggregated KV cache hit rate, and skills invoked via use_skill tool calls.
Frontend Info tab in the right sidebar now displays this data in a compact
key-value layout with a context usage progress bar and clickable skill links.