Closes#12303
### What’s Changed
- Replace auto‐save with explicit Save / Cancel
Webhook forms now use manual “Save” and “Cancel” buttons instead of the
old debounced auto‐save/update.
- Separate “New” and “Detail” routes
Two dedicated paths `/settings/webhooks/new` for creation and
/`settings/webhooks/:webhookId` for editing, making the UX clearer.
- URL hint & normalization
If a user omits the http(s):// scheme, we display a “Will be saved as
https://…” hint and automatically default to HTTPS.
- Centralized validation with Zod
Introduced a `webhookFormSchema` for client‐side URL, operations, and
secret validation.
- Storybook coverage
Added stories for both “New Webhook” and “Webhook Detail”
- Unit tests
Added tests for the new `useWebhookForm` hook
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