feat: trigger audited webhook pings

[giscebot]

Summary

• add an administrator-only action to request a fresh GitHub webhook ping
• validate the stored URL against the exact api.github.com organization/repository hook path before invoking gh api
• audit requested, successful and failed ping actions with the administrator identity
• keep operational CLI errors out of browser responses
• add a Send ping control, progress feedback, delayed refresh and recent administrative actions to hook detail
• document required webhook write permissions for the operational GitHub identity

Validation

• pytest -q — 410 passed
• npm test -- --run — 62 passed
• npm run build

Refs #191

Requested by: @ecarreras