fix(web): settings page layout pass (FE-7)

- Section header (h2 + description) and section blocks as h3; unified
  block padding and title size
- Global settings forms use label-left / control-right rows, stacked
  below md; control width fixed by type (number short, text/select
  medium, wide/textarea full)
- Per-block SaveBar pinned at the block end with dirty hint; naming
  template saves moved from the header to the bar
- Console shell uses overflow-x-clip so the sticky header and sticky
  section nav actually stick; anchor jumps re-align while async content
  loads and land below the header
- Section content uses a single minmax(0,1fr) column so wide tables
  scroll inside their card instead of widening the page
- useSettings fills missing keys from DEFAULT_SETTINGS so an older
  backend no longer crashes the metadata section

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/components/settings/sites.tsx

@@ -105,7 +105,7 @@ const DEFAULTS_CARD: CardSpec = {
 
 export function SitesSection() {
   return (
-    <div className="space-y-6">
+    <div className="grid grid-cols-1 gap-8">
       <div className="pg-slab flex flex-wrap items-center justify-between gap-3 rounded-xl px-4 py-3">
         <p className="text-caption text-muted-foreground">
           站点和凭证在「站点」页管理；单个站点的限流、周期、代理在站点的"编辑"里改。