style(client): normalize font-size across markdown children in message cells

All markdown-emitted elements inside .feed-detail.is-message now
inherit the container's font-size (16px) instead of the browser's
UA defaults. Previously:
- h1-h6 rendered at 2em/1.5em/... (huge in a feed row)
- code used 0.92em (shrunken inline)

Headings are also set inline with margin 0 so prompts like
'# Question' don't break the row flow. Added a blockquote rule
for the same reason. Other child elements fall through the
universal selector.

Author: FulAppiOS

client/src/components/ActivityFeed.css

@@ -306,13 +306,34 @@
 /* Markdown rendering inside message cells: keep everything inline so the
    detail flows as a single line group. `p` is already stripped via a
    fragment renderer in ActivityRow, but guard the rest so lists/code
-   blocks don't blow up the row height. */
+   blocks don't blow up the row height. Every child element inherits
+   the container's font-size so markdown ('**', '#', '`') doesn't
+   balloon headings or shrink inline code. */
+.feed-detail.is-message *,
+.feed-detail.is-message h1,
+.feed-detail.is-message h2,
+.feed-detail.is-message h3,
+.feed-detail.is-message h4,
+.feed-detail.is-message h5,
+.feed-detail.is-message h6 {
+  font-size: inherit;
+  line-height: inherit;
+}
+.feed-detail.is-message h1,
+.feed-detail.is-message h2,
+.feed-detail.is-message h3,
+.feed-detail.is-message h4,
+.feed-detail.is-message h5,
+.feed-detail.is-message h6 {
+  margin: 0;
+  font-weight: bold;
+  display: inline;
+}
 .feed-detail.is-message code {
   background: rgba(255, 255, 255, 0.08);
   padding: 0 4px;
   border-radius: 3px;
   font-family: 'Fira Code', ui-monospace, monospace;
-  font-size: 0.92em;
 }
 .feed-detail.is-message pre {
   margin: 4px 0;
@@ -337,6 +358,12 @@
 }
 .feed-detail.is-message strong { color: #fff; }
 .feed-detail.is-message em { color: #d8d0b8; }
+.feed-detail.is-message blockquote {
+  margin: 0;
+  padding-left: 8px;
+  border-left: 2px solid rgba(255, 255, 255, 0.2);
+  opacity: 0.85;
+}
 
 /* === Group (By Agent) === */
 .feed-group {