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/static/filter.js

@@ -25,9 +25,52 @@ function setActiveTab(el) {
   });
 }
 
+// The chapter-edit form and the delete confirm row are the two per-card
+// disclosure panels; only one makes sense open at a time.
+function closeCardPanels(key) {
+  var form = document.getElementById("chapter-form-" + key);
+  var confirm = document.getElementById("confirm-row-" + key);
+  if (form) form.hidden = true;
+  if (confirm) confirm.hidden = true;
+}
+
 function toggleChapterForm(key) {
   var form = document.getElementById("chapter-form-" + key);
   if (!form) return;
-  form.hidden = !form.hidden;
+  var opening = form.hidden;
+  closeCardPanels(key);
+  form.hidden = !opening;
   if (!form.hidden) form.querySelector("input").focus();
 }
+
+function toggleConfirmRow(key) {
+  var row = document.getElementById("confirm-row-" + key);
+  if (!row) return;
+  var opening = row.hidden;
+  closeCardPanels(key);
+  row.hidden = !opening;
+}
+
+// A failed favourite/chapter/delete request leaves the card in place (htmx
+// does not swap on a non-2xx response) but otherwise gives no sign anything
+// went wrong. Surface it inline instead of leaving the tap looking ignored.
+(function () {
+  function showError(elt, message) {
+    var card = elt.closest(".card");
+    var slot = card && card.querySelector(".error-inline");
+    if (!slot) return;
+    slot.textContent = message;
+    slot.hidden = false;
+    clearTimeout(slot._hideTimer);
+    slot._hideTimer = setTimeout(function () {
+      slot.hidden = true;
+    }, 5000);
+  }
+
+  document.body.addEventListener("htmx:responseError", function (e) {
+    showError(e.detail.elt, "Couldn't save — try again.");
+  });
+  document.body.addEventListener("htmx:sendError", function (e) {
+    showError(e.detail.elt, "No connection — try again.");
+  });
+})();