herdr-muse lifecycle hooks

This uses Herdr's documented
custom integration path: Muse lifecycle
hooks report state over the local Herdr socket with source custom:muse.

Install

One command (Herdr 0.8+):

herdr plugin install akshat12/herdr-muse

then run the Install Muse hooks action. Or without the plugin system:

git clone https://github.com/akshat12/herdr-muse && cd herdr-muse && ./install.sh

Requirements: herdr and python3 on PATH, an existing
~/.config/muse/ (run muse once first). Start a new muse session
after installing — hooks load at session startup.

Compatibility: tested on macOS (Apple Silicon) with Herdr 0.8.2 and
Muse 1.0.2. Linux is declared in herdr-plugin.toml and the code is
portable (bash + python3), but it has not been verified there yet —
reports welcome (see Contributing).

Uninstall anytime: run the Uninstall Muse hooks action, or
./uninstall.sh (removes only Herdr-owned hook entries and the reporter).

How it works

install.sh copies hooks/herdr-muse.py to ~/.config/muse/hooks/ and
registers it for six Muse events (SessionStart, UserPromptSubmit,
PreToolUse, PermissionRequest, Stop, SessionEnd). On each event the
reporter:

1. Finds its Herdr pane by matching its own process ancestry against
   herdr pane process-info (shell PID first, foreground PIDs second,
   realpath-compared cwd as fallback) — Muse hooks run with a cleared
   environment, so HERDR_PANE_ID is unavai