Consolidate config into sky-cam.conf; systemd failure notifications

sky-cam.conf (new)
- Single file replaces mattermost_config.txt reference, notify_config.txt,
  and the hardcoded BASE_DIR/MUSIC_DIR/TIMEZONE scattered across scripts
- Bash-sourceable and Python key=value readable (same format)

All .sh scripts
- source sky-cam.conf at startup; BASE_DIR / MUSIC_DIR from config

sunrise2mm.py
- Reads sky-cam.conf relative to script location; no hardcoded path

notify.sh
- Sources sky-cam.conf; Mattermost credentials come from there directly,
  no separate mattermost_config.txt lookup needed

systemd/sky-cam-notify-failure@.service (new)
- Template unit called by OnFailure= in each service
- Sends notification via notify.sh when any sky-cam job fails
- All three .service units now have OnFailure=sky-cam-notify-failure@%n.service

Removed: notify_config.txt, sky-cam.crontab (superseded)

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

sunrise2mm.py

@@ -2,8 +2,11 @@ import requests
 import os
 from datetime import datetime
 
-# Configuration file path (update the path to where your mattermost_config.txt is located)
-config_file_path = '/home/motion/drives/local-2tb/sunrise-scripts/mattermost_config.txt'
+import pathlib
+
+# Locate sky-cam.conf next to this script (works regardless of cwd).
+_here = pathlib.Path(__file__).resolve().parent
+config_file_path = str(_here / 'sky-cam.conf')
 
 # Function to read configuration from the config file
 def read_config(config_file_path):