test, docs: admin page gate tests and the page's written rules (#102)

- web_test.go walks web.AdminPatterns() rather than naming routes by hand, so a
  new administrative route that forgets requireOwner fails the gate test
  instead of shipping open.
- The harnesses take a LaneReporter; a fake one keeps the page's tests free of
  a poller and a Site.
- backend/AGENTS.md records the adminRoutes/requireOwner rule and the nil-poller
  trap; design-system.md records --patina and the admin page's shape.

docs/design-system.md

@@ -10,7 +10,7 @@ Implemented in:
 
 | Surface | Files |
 | --- | --- |
-| Web UI (login, list, card, empty, errors) | `backend/internal/web/static/style.css`, `backend/internal/web/templates/{app,card,list,login,chrome,icons}.html`, `backend/internal/web/static/filter.js` |
+| Web UI (login, list, card, empty, errors, admin) | `backend/internal/web/static/style.css`, `backend/internal/web/templates/{app,admin,lanes,readers,card,list,login,chrome,icons}.html`, `backend/internal/web/static/filter.js` |
 | Userscript panel (Shadow DOM) | `userscript/manga-bookmark.user.js` — `TEMPLATE` and `CSS` at the bottom of the IIFE |
 
 ## 1. The one idea
@@ -73,6 +73,7 @@ Defined once in `backend/internal/web/static/style.css` `:root`, mirrored in the
 | `--moss` | `#7fae86` | `#3d6c46` | finished accent |
 | `--clay` | `#b5906f` | `#7c5533` | set-chapter accent |
 | `--trash` | `#977671` | `#8c6558` | remove, at rest — icons need 3:1, not 4.5:1 |
+| `--patina` | `#b08a4a` | `#7a5a1e` | admin page only — a Poll Lane needing attention, a Reader whose reports are blocked |
 | `--play-hot-line` | `#3a1d18` | `#f0cfc6` | desktop cell border, play when `.is-new` |
 | `--fav-line` | `#332b14` | `#e3d3a4` | desktop cell border, favourite when on |
 | `--asura` | `#7d93a5` | `#4f6b80` | site tag |
@@ -81,9 +82,12 @@ Defined once in `backend/internal/web/static/style.css` `:root`, mirrored in the
 | `--kagane` | `#9a8aa5` | `#6f5f7d` | site tag |
 | `--hatch` / `--hatch-dim` | 135° 5px stripe | paper stripe | missing-cover slot |
 
-`--slate`/`--moss`/`--clay`/`--brass` are held at the same weight deliberately:
-one accent per action, so a press says which lane it belongs to, with none of
-them competing with ember. Dark is the default (`color-scheme: dark light`);
+`--slate`/`--moss`/`--clay`/`--brass`/`--patina` are held at the same weight
+deliberately: one accent per meaning, so a press says which lane it belongs to,
+with none of them competing with ember. `--patina` is the admin page's only
+colour — system health is neither a new chapter nor destruction, so it borrows
+neither `--ember` nor `--danger`.
+Dark is the default (`color-scheme: dark light`);
 light is a `@media (prefers-color-scheme: light)` override of the same names.
 **Any new colour must be added in both branches** — light is not a filter over
 dark, the hues are re-tuned.
@@ -140,6 +144,14 @@ Recurring specs (copy these rather than inventing sizes):
   main#list      article.card …  |  .empty
 ```
 
+The owner's admin page (`admin.html`) is the same sheet with two sections in
+place of the list — `.lanes` (Poll Lane rows) and `.readers` (the roster) —
+and no library switch: it belongs to neither library, so its topbar carries a
+plain `.ghost.back` link home. Both sections are eyebrow + hairline-separated
+rows, the shape the roster already had as a fold-out. `.lanes` refreshes itself
+every 30s via `hx-get="/ui/admin/lanes"` with `hx-swap="outerHTML"`; the roster
+re-renders only in answer to an action.
+
 **Brand mark**: an inline `<svg class="mark">` (`viewBox="0 0 200 172"`),
 defined once in `chrome.html`'s `mark` template and reused by `app.html` and
 `login.html` so it takes the page's `--ink`/`currentColor`/`--ember` rather