fix: delete issues, ePub reader (JSZip, linear cover, fonts), Pico dialog, UI polish

- Add POST /issues/<id>/delete route with file cleanup
- Fix ePub reader: add JSZip dependency, make cover linear in spine,
  inject system fonts into rendition
- Replace browser confirm() with Pico CSS dialog component
- Fix dashboard button sizing and consistency
- Add favicon, override Pico font stack to suppress Firefox warnings
- Compact issue action buttons

Made-with: Cursor

static/style.css

@@ -1,5 +1,7 @@
 :root {
     --pico-font-size: 16px;
+    --pico-font-family-sans-serif: system-ui, -apple-system, "Segoe UI",
+        Helvetica, Arial, sans-serif, var(--pico-font-family-emoji);
 }
 
 .stats-grid {
@@ -31,6 +33,18 @@
     display: flex;
     gap: 0.5rem;
     flex-wrap: wrap;
+    align-items: center;
+    margin-bottom: 1.5rem;
+}
+.action-buttons form { margin: 0; }
+.action-buttons a[role="button"],
+.action-buttons button {
+    white-space: nowrap;
+    padding: 0.5rem 1rem;
+    font-size: 0.95rem;
+    line-height: 1.4;
+    margin: 0;
+    width: auto;
 }
 
 .hidden { display: none !important; }
@@ -123,6 +137,29 @@ nav .brand { font-weight: bold; font-size: 1.1rem; }
     border-bottom: 1px solid var(--pico-muted-border-color);
 }
 
+/* Issue actions */
+.issue-actions {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 0.35rem;
+    align-items: center;
+}
+.issue-actions form { margin: 0; }
+.issue-actions a[role="button"],
+.issue-actions button {
+    padding: 0.25rem 0.6rem;
+    font-size: 0.8rem;
+    line-height: 1.4;
+    margin: 0;
+    width: auto;
+}
+.btn-danger { color: var(--pico-del-color); }
+.btn-danger-fill {
+    background: var(--pico-del-color);
+    border-color: var(--pico-del-color);
+    color: #fff;
+}
+
 /* Consistent interactive elements */
 button, [role="button"],
 input[type="submit"],