Add agent sessions panel

[accessd]

What changed

• Add a right-side fzf panel for live Claude Code, Codex, OpenCode, Pi, Aider, and Cursor panes.
• Group panes by agent state and working directory, with pinning and pane navigation.
• Make Alt+i show the current tmux session and Alt+Shift+i show every session.
• Restore Claude's running state after successful or failed tool use so resolved prompts do not remain needs-input.
• Document the behavior and add isolated tmux regression coverage.

Why

The status indicator only describes one pane. There was no server-level view of active agent work, and Claude could retain stale needs-input state after a prompt or permission was resolved because no post-tool hook restored running.

Impact

Users can inspect current-session agents by default, switch to a server-wide view when needed, pin important panes, and jump directly to a selected agent. Panel membership still comes from live pane processes, while hooks supply richer state.

Validation

• ./tests/run-all.sh
• bash -n agent-indicator.tmux scripts/*.sh install.sh setup.sh tests/*.sh tests/lib/*.sh
• shellcheck -x -S warning agent-indicator.tmux scripts/*.sh install.sh setup.sh tests/*.sh tests/lib/*.sh
• git diff --check

Manual follow-up

• Add a final panel screenshot after UX verification.