Copy tmux debug snapshot

[semantic-craft]

Parent

Parent: #2

What to build

Add a lightweight debug snapshot action that copies the current tmux/app state as text. This is for diagnosing cases where the tmux CLI sees sessions but the UI appears stale or wrong.

The snapshot should be built from existing app state and tmux read commands. It should be copyable and human-readable, not a new logging subsystem.

Acceptance criteria

• The user can trigger a debug snapshot from an appropriate native UI surface.
• The snapshot includes the tmux binary path and resolved socket path.
• The snapshot includes last refresh status, loading/error state, and session/window/pane counts known to the app.
• The snapshot includes a concise sessions/windows/panes summary using stable tmux IDs and names.
• The snapshot includes tmux command/read failures if they occur while building the snapshot.
• The snapshot is copied to the clipboard and confirms success with existing toast/status behavior.
• Snapshot generation does not mutate tmux state and does not add persistent logs.
• Manual verification includes copying a snapshot while a known tmux session is running and confirming the text contains that session.

Blocked by

• Finish trustworthy refresh state #3