feat: repli des articles en mode lecture avec bouton Lire plus

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

static/read-more.css

@@ -0,0 +1,24 @@
+/* Read More — collapsed articles in reader view.
+ * max-height only: the article must keep a non-zero height so that
+ * FreshRSS still marks it as read when scrolled past. */
+.flux .text.read-more-collapsed {
+	max-height: var(--read-more-height, 250px);
+	overflow: hidden;
+	position: relative;
+}
+
+.flux .text.read-more-collapsed::after {
+	content: "";
+	position: absolute;
+	left: 0;
+	right: 0;
+	bottom: 0;
+	height: 4em;
+	background: linear-gradient(to bottom, transparent, var(--frss-background-color, #fff));
+	pointer-events: none;
+}
+
+.flux .read-more-btn {
+	display: block;
+	margin: 0.5em auto 1em;
+}