Owner-only admin page: Reader roster plus Poll Lane status (#102) (#107)

Closes #102.

The only operational surface was /healthz and a fold-out roster inside the owner's own reading page. This adds /admin: an owner-only page carrying the Reader roster and one row per Poll Lane.

- **Poller seam.** `latest.Poller` records each Lane's last pass (`Site`, `Due`, `Checked`, `LastRun`, `Gap`, `Clamped`, `Browser`) and answers `LaneStatus()`; the page reads that snapshot, never a table. A pass that returns before computing its figures (refusal backoff, sidecar down) carries the previous pass's figures forward rather than recording zeroes, and a Lane that has never reached a pace renders no gap at all. Refusal and sidecar reachability are derived at snapshot time.
- **Owner gate at registration.** Every route reaching past the acting Reader lives in `adminRoutes()` and is wrapped in `requireOwner` when it is registered, so a missing gate is visible in the route list rather than hidden in a handler. `web.AdminPatterns()` is what the gate test walks, so a new route cannot be added without being tested. A non-owner gets 404, never 403.
- **Nil poller is a first-class state.** `main.newRouter` takes the reporter as an interface and converts a nil `*Poller` to a nil interface; no poller and no completed pass both render "No data yet" with the reason spelled out, rather than confident zeroes.
- **Roster moved** off the reading page onto /admin, with the Sighting counters and a confirm-gated `Clear marks` control. #103 fills those counters, so on delivery they read zero for everyone - deliberate ordering.
- **One accent, `--patina`** (verdigris, both colour branches): the far side of the wheel from ember's crimson and clear of the archive blue. Ember still means new chapter only; revocation still wears --danger.

Verification: `go vet ./...` and `go test ./...` green (Docker-backed); admin page screenshotted at 1100px and 390px in both colour schemes. Reviewed on both axes (spec, standards); findings on the accent hue, zero-figure honesty and three tests that could not fail are fixed in 58014eb.
Reviewed-on: #107
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/AGENTS.md

@@ -211,6 +211,25 @@ Guidance for OpenCode (and Claude Code) working under `backend/`. See root `AGEN
   `POST /rotate-token` (atomic epoch bump + hash
   rewrite; invalidates every installed copy, so the panel warns to reinstall
   on all devices).
-  Owner-only `POST /readers/{id}/revoke` (drops one Reader's session rows and
-  re-renders the `readers` panel; 404 for any non-owner) is the only route that
-  reaches across Readers.
+- **Owner-only admin page (`internal/web/admin.go`, issue #102):** `GET /admin`
+  carries the Reader roster (sessions, Sighting counters, `POST
+  /readers/{id}/revoke` and `POST /readers/{id}/clear-marks`) and Poll Lane
+  status (`GET /ui/admin/lanes`, self-refreshing every 30s). Every route that
+  reaches past the acting Reader is listed in `adminRoutes()` and wrapped in
+  `requireOwner` at registration — add a route there, not a check inside a
+  handler; `web.AdminPatterns()` is what the gate test walks. A non-owner gets
+  404, never 403. Lane figures come from the running poller through the
+  `web.LaneReporter` seam (`latest.Poller.LaneStatus`), never from a table: a
+  nil reporter or a Lane that has not finished a pass renders "no data yet"
+  rather than zeroes. `main.newRouter` takes the reporter as an interface and
+  converts a nil `*Poller` to a nil interface — a typed nil would make the page
+  claim a poller exists.
+  The one owner comparison left outside `requireOwner` is in `index`
+  (`view.Owner = readerID == h.store.OwnerID()`): it gates a link, not an
+  endpoint, so it is a rendering decision a registration-time wrapper cannot
+  express — do not "unify" it into the gate.
+  A Lane pass that returns before computing its figures (refusal backoff,
+  sidecar down) carries the previous pass's due count and gap forward rather
+  than recording zeroes; a Lane that has never reached a pace renders no gap at
+  all. `Checked` next to `Due` is what separates a stopped Lane from a quiet
+  one, so neither figure may be dropped from the row.