feat(ui): touch-friendly message actions, header spacing, scroll-to-latest (#402)

ui/assets/main.css

@@ -111,3 +111,36 @@
     outline: 2px solid currentColor;
     outline-offset: 1px;
 }
+
+/* Touch-only message action affordance (freenet/river#402).
+ *
+ * The per-message hover action bar (reply / edit / delete) is built with
+ * Tailwind `group-hover:` utilities, which Tailwind v4 automatically wraps in
+ * `@media (hover: hover)`. On a touch device (phone, tablet) there is no hover
+ * pointer, so that bar can NEVER become visible and touch users have no way to
+ * reach reply / edit / delete / react.
+ *
+ * `.touch-actions` is the exact complement: hidden by default (so mouse users
+ * keep the clean hover-reveal desktop UI) and shown only where `hover: none`
+ * matches — i.e. precisely the devices where the hover bar cannot appear. It
+ * decorates the always-visible kebab (⋮) button that opens the touch action
+ * menu. */
+.touch-actions {
+    display: none;
+}
+
+@media (hover: none) {
+    .touch-actions {
+        display: flex;
+    }
+
+    /* The hover action bar (reply/edit/delete) is opacity-0 until hovered, but
+     * an opacity-0 element still captures taps. On a touch device (no hover) it
+     * can never become visible, so make it non-interactive there; otherwise a
+     * tap on the gutter where it sits would fire an invisible reply/edit/delete.
+     * Left interactive on desktop (@media hover:hover) so slow mouse travel
+     * across the gap to the bar still works. (#402) */
+    .hover-actions {
+        pointer-events: none;
+    }
+}