feat(planner): restyle Export + SaveToJournal buttons on tokens

Bring the two slotted topbar actions onto the design system so the bar
reads as one cohesive surface:

- SaveToJournalButton: primary Button primitive; "saved" uses the
  accent, error uses a new --color-danger token, and the return link
  gets secondary token styling.
- ExportButton: token split-button (secondary look, chevron icon,
  single divider) and a token dropdown menu (raised surface, soft
  shadow, muted descriptions).
- New --color-danger token (#a03c3c, the no-go hue at full strength)
  for error text.

Behavior and i18n unchanged.

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

packages/ui/src/theme.css

@@ -41,6 +41,7 @@
   --color-stop-border: rgba(139, 109, 58, 0.25);
 
   /* ── Danger / no-go ── */
+  --color-danger: #a03c3c; /* solid danger — error text, matches the no-go hue */
   --color-nogo: rgba(160, 60, 60, 0.12);
   --color-nogo-border: rgba(160, 60, 60, 0.3);