[bug] E4-6: TmuxCaptureCache has no eviction — dead session entries grow indefinitely

[OneStepAt4time]

Finding

ID: M-1 | Severity: 🟡 LOW

Dead sessions' entries remain in the TmuxCaptureCache map indefinitely. With many short-lived sessions, the map grows without bound.

Fix Required

Add a periodic (5-minute) eviction pass that removes entries for sessions no longer in state.sessions.

Files: src/tmux-capture-cache.ts

Acceptance Criteria

After killing 100 sessions, TmuxCaptureCache size returns to 0.

Milestone

M-E4: Reliability & Robustness