* test: reproduce issue #786
* fix: load extra headers from settings (closes#786)
* test: cover extra header precedence and redaction
* fix: redact persisted extra headers in diagnostics
* test: cover runner extra header identity
* fix: restart runner when extra headers change
- Add settings.json column to environment variables table with key name mappings
- Document missing ENV variables: TELEGRAM_BOT_TOKEN, TELEGRAM_NOTIFICATION,
HAPI_RELAY_FORCE_TCP, VAPID_SUBJECT
- Add settings.json example with configuration priority explanation
- Create JSON Schema file for settings.json validation and editor autocompletion
with all fields, descriptions, and ENV variable references
clsoe #113