Show an event's entrypoint and request headers (closes #389)

An expanded event in the event log and the event's own page now show
the entrypoint the event arrived at (its description, "Entrypoint"
when it has none, or "deleted entrypoint"; never its URL) and the
full request headers, one per line, sorted by name. Both pages draw
them through one shared template, event_request.html. The event
columns now load entrypoint_id and headers, and the webhook's
entrypoints are read once per page.

Model: opus-5-5

templates/event_detail.html

@@ -50,6 +50,15 @@
         </dl>
     </div>
 
+    <div class="card mt-6">
+        <div class="p-4 border-b border-gray-200">
+            <h2 class="text-lg font-medium text-gray-900">Request</h2>
+        </div>
+        <div class="p-4">
+            {{template "event_request" .}}
+        </div>
+    </div>
+
     <div class="card mt-6">
         <div class="p-4 border-b border-gray-200">
             <h2 class="text-lg font-medium text-gray-900">Body</h2>

templates/event_request.html

@@ -0,0 +1,16 @@
+{{define "event_request"}}
+<!-- The entrypoint an event arrived at and its request headers, as
+     handlers.EventLogView carries them: the same in the event log and
+     the event's own page. The entrypoint's URL is never shown. -->
+<div class="space-y-2 text-xs">
+    <p class="text-gray-500">Arrived at <span class="text-gray-900">{{.Entrypoint}}</span></p>
+    {{if .Headers}}
+    <p class="text-gray-500">Request headers</p>
+    <div class="rounded-md border border-gray-200 bg-white p-2 font-mono text-gray-700 break-all">
+        {{range .Headers}}<div>{{.}}</div>{{end}}
+    </div>
+    {{else}}
+    <p class="text-gray-500">No request headers.</p>
+    {{end}}
+</div>
+{{end}}

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}}