Add endpoint deletion

The endpoints screen could only create and edit servers, so a mistyped
or retired endpoint stayed in the list forever.

Tasks reference endpoints without ON DELETE CASCADE, so a referenced
endpoint is refused with 409 and a count of the tasks using it rather
than cascading away migration history. The foreign-key violation is
mapped to the same status to cover a task created between check and
delete.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/src/api.ts

@@ -82,6 +82,8 @@ export const updateEndpoint = (
   body: { role_label: string; host: string; port: number; tls_mode: TLSMode },
 ) => api(`/api/endpoints/${id}`, { ...jsonBody(body), method: 'PUT' })
 
+export const deleteEndpoint = (id: number) => api(`/api/endpoints/${id}`, { method: 'DELETE' })
+
 export const deleteTask = (id: number) => api(`/api/tasks/${id}`, { method: 'DELETE' })
 
 export const deleteAccount = (taskId: number, accountId: number) =>