Cinder pass across /admin, the login gate, and the library's a11y floor (#177)

One commit (`af07314`), three strands of browser-UI work against one design system. `docs/design-system.md` was updated to match the CSS, not the reverse.

## Library (Reader-facing)

Findings came out of a two-axis design review of the library surface; the fixes are the P1/P2 set plus the cheap P3s.

- **`.chrome` sticks at `top: 0`.** Search and the tab row were unreachable three screens into a 300-item library — exactly where they earn their keep. Everything above them (`.topbar`, `.keyrow`, `.recent`) still scrolls away on purpose: another 150px of permanent chrome on an 844px phone costs more than re-scrolling for an icon reminder.
- **One `:focus-visible` ring** (`2px solid var(--paper)`, offset 2px) on the nine controls that defined none and fell back to the UA blue — a colour tuned for neither branch of this palette. `.searchbar` keeps its `:focus-within` border recolour as a resting cue but no longer stands in for the ring.
- **Mono labels lift 10px → 11px** everywhere (nine rules). PRODUCT.md names night reading and glare as the usage scene; 10px small-caps was the one place taste overrode the brief. 11px is now a documented floor.
- **A card in flight past 2s says `Saving…` and carries `aria-busy`.** htmx sets neither, so the wait — up to its own 15s timeout, and this app is used on a phone in dead zones — was silent in both the visual and the assistive channel. Deliberately `--mute`, not `--ember`: ember means "new chapter" and nothing else.
- **Titles clamp at 3 lines**; `.is-new .title` takes `width: fit-content`, or `-webkit-box` stretches the ember underline past the text it is supposed to be sized to.
- `.libswitch a` reaches a real 44px under `(pointer: coarse)` — padding plus an 11px line landed at 43.

## /admin

- Overview routes into Lanes when a lane is unhealthy, prefixes each figure with its column word on the phone layout that drops the `thead`, labels state cells for a screen reader, and has an empty state where the sites table previously assumed rows.
- The admin shell picks up the library's chrome: htmx 15s timeout, the shared `#notice` slot, `#sr-announce`, `filter.js`.
- `admin_render_test.go` and `card_render_test.go` render the templates directly, so markup regressions in either surface fail without a browser.

## Login

`DISCORD_GUILD_NAME` (optional) names the community on the login screen and in the refusal message, so a stranger knows which Discord to ask for an invite. Unset degrades to a generic label. Neither form names the numeric guild id — that was never actionable, and the gate still reveals nothing about whether a given guild exists.

## Handlers

`maxChapterNum` (9999) now bounds **both** typed-chapter paths. `uiChapter` and `adminSeriesCorrectLatest` each parsed a `float64` with no ceiling, so a hand-rolled POST stored `1e308` and every later reader of that row — the poller's `HasNewChapter` comparison, the display string — inherited it. Matches the `max` on the card's chapter input. The API PUT path is deliberately untouched: it carries the userscripts' own scraped numbers, not typed input.

## Verification

- `cd backend && go test ./...` green (Docker-backed `pgtest`). `TestChapterOverrideRejectsBadInput` gained `"10000"` and `"1e5"` — both parse fine as `float64`, so they only fail if the bound exists.
- Visual: 390×844 dark + light, 1000px and 1440px (`zoom: 1.2`) desktop, against the real templates + real CSS. Measured `chromeTop = 0` at `scrollY 950`, `2px solid rgb(242,236,229)` rings, `content: "Saving…"` at `opacity: 1` after 2.4s, `aria-busy` `true` during / cleared after, `libswitchH = 44` in a `hasTouch` context, no horizontal overflow at either width.
- `detect.mjs` on `templates/`: `[]`, exit 0.

## Note on shape

The three strands landed as one commit because `admin_series.go` and `style.css` each carry hunks from more than one of them; splitting cleanly would have needed hunk-level surgery. Say the word if you want it split before merge.

Reviewed-on: #177
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/internal/web/templates/app.html

@@ -5,6 +5,11 @@
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
   <meta name="color-scheme" content="dark light">
+  {{/* htmx defaults to no timeout, so a phone that walks into a dead zone
+       leaves the XHR open forever and the card it came from keeps its busy bar
+       and its disabled actions until a reload. 15s is well past any response
+       this deployment produces. */}}
+  <meta name="htmx-config" content='{"timeout":15000}'>
   <title>BookmarkManager</title>
   <link rel="icon" href="/static/logo.svg" type="image/svg+xml">
   <link rel="stylesheet" href="/static/style.css">
@@ -53,34 +58,39 @@
     <a href="{{.PageURL "all"}}" class="{{if eq .Tab "all"}}active{{end}}"
        {{if eq .Tab "all"}}aria-current="page"{{end}}
        hx-get="{{.ListURL "all"}}" hx-target="#list" hx-swap="innerHTML"
-       hx-push-url="{{.PageURL "all"}}" hx-on::after-request="setActiveTab(this)">All</a>
+       hx-push-url="{{.PageURL "all"}}" hx-on::after-request="if (event.detail.successful) setActiveTab(this)">All</a>
     {{/* The one bucket novels do not have: without a poller-fed "what is out
          that I have not read", the tab would only ever restate All. */}}
     {{if eq .Lib "manga"}}
     <a href="{{.PageURL "new"}}" class="tab-new {{if eq .Tab "new"}}active{{end}}"
        {{if eq .Tab "new"}}aria-current="page"{{end}}
        hx-get="{{.ListURL "new"}}" hx-target="#list" hx-swap="innerHTML"
-       hx-push-url="{{.PageURL "new"}}" hx-on::after-request="setActiveTab(this)">Updated
+       hx-push-url="{{.PageURL "new"}}" hx-on::after-request="if (event.detail.successful) setActiveTab(this)">Updated
       {{template "newcount" .}}</a>
     {{end}}
     <a href="{{.PageURL "fav"}}" class="{{if eq .Tab "fav"}}active{{end}}"
        {{if eq .Tab "fav"}}aria-current="page"{{end}}
        hx-get="{{.ListURL "fav"}}" hx-target="#list" hx-swap="innerHTML"
-       hx-push-url="{{.PageURL "fav"}}" hx-on::after-request="setActiveTab(this)">Favourites</a>
+       hx-push-url="{{.PageURL "fav"}}" hx-on::after-request="if (event.detail.successful) setActiveTab(this)">Favourites</a>
     <a href="{{.PageURL "archived"}}" class="{{if eq .Tab "archived"}}active{{end}}"
        {{if eq .Tab "archived"}}aria-current="page"{{end}}
        hx-get="{{.ListURL "archived"}}" hx-target="#list" hx-swap="innerHTML"
-       hx-push-url="{{.PageURL "archived"}}" hx-on::after-request="setActiveTab(this)">Archived</a>
+       hx-push-url="{{.PageURL "archived"}}" hx-on::after-request="if (event.detail.successful) setActiveTab(this)">Archived</a>
   </nav>
   </div>
 
+  {{/* Where a failure with no card to sit in gets reported: a tab switch, a
+       rotation, an expired session. filter.js fills it and unhides it. */}}
+  <p class="notice" id="notice" role="status" hidden></p>
+<div id="sr-announce" class="sr-only" role="status" aria-live="polite" aria-atomic="true"></div>
+
   {{template "setup" .}}
 
   {{template "keyrow" .}}
 
   {{template "recent" .}}
 
-  <main id="list" class="list">
+  <main id="list" class="list" tabindex="-1">
     {{template "list" .}}
   </main>
 </div>