feat: Active sessions panel, per-session controls, and add-from-active flowFeat/active sessions

[k161196]

Summary

Adds a dedicated Active Sessions list, surfaces per-session metadata (keys/forwards), and
enables killing a selected active SSH session. Active entries are derived from running
ssh processes and are not persisted; use the add-from-active flow to create config
entries.

Changes

• UI: add bottom Active Sessions list; keep main list for configured servers only
• UI: enable kill on active list (K) and add-from-active prefill; disable edit for active
  entries
• Services: implement ListActiveSessions; parse running ssh processes with PID, keys, and
  forwarding
• Domain: track active PID to target kills per session

Testing

• make build
• make run (manual: verify active sessions list, kill on active, add-from-active)