feat(web,latest): pause and resume one Site's Lane with a mandatory expiry (#147)

Two owner-gated POST routes write the durable poll_lanes pause stamp the
poller's top-of-pass gate already reads: /admin/lanes/{site}/pause validates
the duration against the fixed 1h/6h/24h allow-list and the Site against the
registry, and /admin/lanes/{site}/resume zeroes the stamp. Both cap the form
body like the API path, answer with the freshly rendered Lanes block, and
never command the poller — the pause is a fact about the Site, so it
survives a restart. The Lanes page's c-ctrl slot now carries the pausebar:
Resume while paused, the duration select plus Pause while running, with the
paused phrase read from the live poll_lanes stamp so a press renders as
paused with no pass having run. Tests cover the round trips, rejections,
body caps, the pause-before-refusal ordering, fresh-poller survival, resume
restoring the full queue, and acquisition being unaffected.

backend/internal/web/templates/lanes.html

@@ -32,7 +32,24 @@
       <span>{{.Gap}}</span>
       <span>ran {{.Ran}}</span>
       <span class="c-skip">{{if .HasChips}}{{range $i, $c := .Chips}}{{if $i}}<span class="mark-faint"> · </span>{{end}}<span class="mark">{{$c.Name}} {{$c.Count}}</span>{{end}}{{else}}<span class="mark-faint">none observed</span>{{end}}{{if .StatePhrase}} · <span class="{{if .StateGood}}ok{{else}}bad{{end}}">{{.StatePhrase}}</span>{{end}}</span>
-      <span class="c-ctrl"></span>
+      {{/* The pause control lives in the one slot the design leaves for it:
+           a running Lane offers the three durations and Pause; a paused Lane
+           offers Resume in the same place. Pause is not destruction — it
+           takes nothing away and reverses in one press — so neither wears a
+           confirm row or the danger accent. The form wraps the select so the
+           offered duration travels with the press. */}}
+      <span class="c-ctrl">{{if .Paused}}<span class="pausebar">
+        <form hx-post="/admin/lanes/{{.Site}}/resume" hx-target="#lanes" hx-swap="outerHTML">
+          <button type="submit" class="ghost">Resume</button>
+        </form>
+      </span>{{else}}<span class="pausebar">
+        <form hx-post="/admin/lanes/{{.Site}}/pause" hx-target="#lanes" hx-swap="outerHTML">
+          <select name="duration" aria-label="Pause duration">
+            <option>1h</option><option selected>6h</option><option>24h</option>
+          </select>
+          <button type="submit" class="ghost">Pause</button>
+        </form>
+      </span>{{end}}</span>
     </div>
     {{end}}
   </div>