feat(web): updated tab, inline errors, card craft

Adds the Updated tab (series with an unread chapter) with its own empty
state, so "what's new" no longer means scanning the whole list.

A failed favourite/chapter/delete previously looked like an ignored tap:
htmx does not swap on a non-2xx response and nothing else said so. Errors
now surface inline on the card. The two per-card panels (chapter edit,
delete confirm) also close each other.

Mobile fixes, all measured at 360/390px rather than eyeballed:
.chapter-form and .confirm-row now wrap so the hint and the prompt take
their own row, and the number input shrinks (flex-basis 0) instead of
holding its ~20ch intrinsic width. Before this the Save button sat off
screen — 97px of page overflow at 390px, 127px at 360px — which broke
correcting a chapter number on the one device class this is built for.

Emoji glyphs replaced with inline SVG on currentColor: each rendered in a
different face at a different weight and colour, ignoring the card's own
type and colour system. No icon font or library.

Series with no scraped og:image render a title-initial monogram instead
of a blank rectangle that read as a cover still loading.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/templates/app.html

@@ -25,6 +25,9 @@
     <a role="tab" href="/?tab=all" class="{{if eq .Tab "all"}}active{{end}}"
        hx-get="/ui/list?tab=all" hx-target="#list" hx-swap="innerHTML"
        hx-push-url="/?tab=all" hx-on::after-request="setActiveTab(this)">All</a>
+    <a role="tab" href="/?tab=new" class="tab-new {{if eq .Tab "new"}}active{{end}}"
+       hx-get="/ui/list?tab=new" hx-target="#list" hx-swap="innerHTML"
+       hx-push-url="/?tab=new" hx-on::after-request="setActiveTab(this)">Updated</a>
     <a role="tab" href="/?tab=fav" class="{{if eq .Tab "fav"}}active{{end}}"
        hx-get="/ui/list?tab=fav" hx-target="#list" hx-swap="innerHTML"
        hx-push-url="/?tab=fav" hx-on::after-request="setActiveTab(this)">Favourites</a>
@@ -36,7 +39,11 @@
     <div class="recent-strip">
       {{range .Recent}}
       <a class="recent-card" href="{{.ContinueURL}}" target="_blank" rel="noopener noreferrer">
-        {{if .Cover}}<img src="{{.Cover}}" alt="" loading="lazy">{{end}}
+        <span class="recent-cover">
+          {{if .Cover}}<img src="{{.Cover}}" alt="" loading="lazy">
+          {{else}}<span class="cover-blank" aria-hidden="true">{{.Initial}}</span>{{end}}
+          {{if .HasNewChapter}}<span class="new-ribbon new-ribbon-sm">New</span>{{end}}
+        </span>
         <span class="recent-title">{{.Title}}</span>
         <span class="recent-chapter">Ch {{.LastChapter}}</span>
       </a>