Move webhook pages to /hook/ID and inbound URLs to /h/UUID (closes #367)

The webhook page and everything under it move from /source/ID to
/hook/ID, the list and new-webhook form to /hooks and /hooks/new, and
the event log from .../logs to /hook/ID/events, body download
included. Entrypoint URLs move from /webhook/UUID to /h/UUID, and the
webhook page shows only that form. The old paths are gone.

Links, redirects, form actions, tests, comments and the README follow.
Go identifiers and template file names are unchanged. A new route test
posts to the entrypoint URL the webhook page shows and checks that the
receiver rate limit applies to it.

Model: opus-5-5

templates/source_edit.html

@@ -5,7 +5,7 @@
 {{define "content"}}
 <div class="max-w-2xl mx-auto px-6 py-8">
     <div class="mb-6">
-        <a href="/source/{{.Webhook.ID}}" class="text-sm text-primary-600 hover:text-primary-700">&larr; Back to {{.Webhook.Name}}</a>
+        <a href="/hook/{{.Webhook.ID}}" class="text-sm text-primary-600 hover:text-primary-700">&larr; Back to {{.Webhook.Name}}</a>
         <h1 class="text-2xl font-medium text-gray-900 mt-2">Edit Webhook</h1>
     </div>
 
@@ -14,7 +14,7 @@
         <div class="alert-error">{{.Error}}</div>
         {{end}}
 
-        <form method="POST" action="/source/{{.Webhook.ID}}/edit" class="space-y-6">
+        <form method="POST" action="/hook/{{.Webhook.ID}}/edit" class="space-y-6">
             <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
             <div class="form-group">
                 <label for="name" class="label">Name</label>
@@ -34,7 +34,7 @@
 
             <div class="flex gap-3">
                 <button type="submit" class="btn-primary">Save Changes</button>
-                <a href="/source/{{.Webhook.ID}}" class="btn-secondary">Cancel</a>
+                <a href="/hook/{{.Webhook.ID}}" class="btn-secondary">Cancel</a>
             </div>
         </form>
     </div>