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

internal/handlers/target_edit.go

@@ -47,7 +47,7 @@ type targetEditView struct {
 //
 // This page is the one place the full destination URL and header
 // values are shown. It is reachable only through the
-// /source/{sourceID} route group, which supplies RequireAuth and
+// /hook/{sourceID} route group, which supplies RequireAuth and
 // NoCache, and only for a target of a webhook the session's user
 // owns; masking (delivery.TargetView) is unchanged everywhere else.
 func (h *Handlers) HandleTargetEdit() http.HandlerFunc {
@@ -163,7 +163,7 @@ func (h *Handlers) applyTargetEdit(
 	}
 
 	http.Redirect(
-		w, r, "/source/"+webhook.ID, http.StatusSeeOther,
+		w, r, "/hook/"+webhook.ID, http.StatusSeeOther,
 	)
 }