Show an event's entrypoint and request headers in the event log and on its page (closes #389)

The receiver stored each event's request headers and entrypoint, but no page showed them, so with several entrypoints the operator could not tell which sender sent an event. An expanded event in the event log, and the event's own page, now show the entrypoint by its description ("Entrypoint" without one, "deleted entrypoint" once deleted), never its URL, and the headers as one escaped block, sorted, whitespace kept. A resubmitted copy says the request it copies arrived there. The event log reads at most 32 KiB of headers per event, the body's limit, and links to the event's page beyond it. Both pages share one template, `event_request.html`.

Model: opus-5-5

templates/source_logs.html

@@ -55,6 +55,9 @@
                             <button type="submit" class="btn-small" title="Submit this event again as a new event, to every currently active target">Resubmit</button>
                         </form>
                     </div>
+                    <div class="mb-3">
+                        {{template "event_request" .}}
+                    </div>
                     {{template "event_body" .Body}}
 
                     {{if .Deliveries}}