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/web.go

@@ -35,11 +35,21 @@ type webHandler struct {
 
 // listView is what every list-rendering template receives.
 type listView struct {
-	Tab    string // "all" or "fav"
+	Tab    string // "all", "fav", or "new"
 	Recent []Bookmark
 	Items  []Bookmark
 }
 
+// Initial is the monogram the templates show in place of a cover when the
+// source site never gave us an og:image. First rune, uppercased; "?" when even
+// the title is missing, so the slot is never empty.
+func (b Bookmark) Initial() string {
+	for _, r := range b.Title {
+		return strings.ToUpper(string(r))
+	}
+	return "?"
+}
+
 // loginView is what the login template receives.
 type loginView struct {
 	Error string
@@ -150,14 +160,22 @@ func (h *webHandler) buildListView(tab string) (listView, error) {
 	}
 
 	items := all
-	if tab == "fav" {
+	switch tab {
+	case "fav":
 		items = []Bookmark{}
 		for _, b := range all {
 			if b.Favorite {
 				items = append(items, b)
 			}
 		}
-	} else {
+	case "new":
+		items = []Bookmark{}
+		for _, b := range all {
+			if b.HasNewChapter() {
+				items = append(items, b)
+			}
+		}
+	default:
 		tab = "all"
 	}
 	return listView{Tab: tab, Recent: recent, Items: items}, nil