v0.31.2: landing welcome panel spacing

Visual-only patch. The "/" welcome read-view was jammed against the
catalog divider with no top offset and loose paragraph rhythm: the
.main-pane §8 override (padding:0; display:flex) shadows the padded
read-view rule, so the pane gives no padding, and .welcome (max-width
only) never compensated. The welcome surface now owns its breathing
room — 56px top / 48px side gutters, a 680px measure, a text-3xl hero,
and even --space-8 paragraph spacing at --leading-relaxed. Covers both
the signed-out and signed-in welcome.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "rfc-app-frontend",
   "private": true,
-  "version": "0.31.1",
+  "version": "0.31.2",
   "type": "module",
   "scripts": {
     "dev": "vite",