review: verdigris patina, honest Lane figures, tests that can fail (#102)

Two-axis review found the shipped colour and three weak tests.

- --patina was a warm gold at the same hue family as --brass; the spec
  asked for a cool blue-green so an unhealthy Lane is unmistakably not
  ember. Now verdigris in both branches, with docs/design-system.md
  stating why the far side of the wheel is the point.
- A Lane pass that returns before computing its figures carries the
  previous pass's due count and gap forward instead of recording zeroes,
  and Checked rides beside Due so a stopped Lane is distinguishable from
  a quiet one.
- TestAdminPageWithoutAPollerSaysSo now separates the two causes it
  conflated, TestOwnerClearsReaderMarks seeds real counters so the
  clearing assertion can fail, and TestLaneStatus asserts Checked and
  the carry-forward.
- backend/AGENTS.md records the one deliberate owner comparison outside
  requireOwner and the carry-forward rule.

backend/internal/web/templates/lanes.html

@@ -7,7 +7,7 @@
      a Site absent from Rows has not completed a pass since the last restart,
      which the empty state must say — zeroes would read as a stopped Lane. */}}
 {{define "lanes"}}
-<section class="lanes" id="lanes" aria-live="polite"
+<section class="lanes" id="lanes"
          hx-get="/ui/admin/lanes" hx-trigger="every 30s" hx-swap="outerHTML">
   <h2>Poll Lanes</h2>
   {{if .Rows}}
@@ -16,11 +16,13 @@
     <li{{if .Attention}} class="attention"{{end}}>
       <span class="lane-site">{{.Site}}</span>
       <span class="lane-fact">{{.Due}} due</span>
+      <span class="lane-fact">{{.Checked}} checked</span>
       <span class="lane-fact">ran {{.Ran}}</span>
-      <span class="lane-fact">gap {{.Gap}}</span>
+      {{if .Gap}}<span class="lane-fact">gap {{.Gap}}</span>{{end}}
       {{if .Clamped}}<span class="lane-mark">gap at floor</span>{{end}}
       {{if .Refusing}}<span class="lane-mark">refusing</span>{{end}}
       {{if .BrowserLost}}<span class="lane-mark">no browser</span>{{end}}
+      {{if .Stalled}}<span class="lane-mark">not checking</span>{{end}}
     </li>
     {{end}}
   </ul>
@@ -28,9 +30,12 @@
   <p class="setup-copy">No data yet — no Lane has completed a pass since the
     backend started.</p>
   {{end}}
-  <p class="setup-copy lane-browser">Browser sidecar:
+  <p class="setup-copy lane-browser">
+    {{if .PollerOff}}Polling is switched off in this deployment: no Lane runs,
+    and Latest Chapter comes from the userscripts alone.
+    {{else}}Browser sidecar:
     {{if not .BrowserConfigured}}not configured — comix, kagane and novelfull
     pages are not fetched through it{{else if .BrowserReachable}}reachable
-    {{else}}unreachable{{end}}.</p>
+    {{else}}unreachable{{end}}.{{end}}</p>
 </section>
 {{end}}