fix(dashboard): primary mission CTA, auto-select first, richer empty state

- Promote the sidebar "Plan New Mission" CTA to a btn-primary (matching the
  chat sidebar's "New Chat") and drop the dashed icon buttons; full-width
  progress bar and Activity row each get their own line in the card.
- Auto-select the first mission in the inline desktop view so users land
  in detail rather than the empty placeholder. Skipped in mobile and the
  standalone modal so existing flows and unit tests stay intact.
- Replace the bare "No missions yet" line with a richer empty state that
  explains what missions are and offers an inline Plan New Mission CTA.
- Guard loadMissionDetail against malformed responses (missing milestones)
  so racing fetch fallbacks don't crash the detail render.
- Update three MissionManager tests to match the new copy/structure.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/dashboard/app/components/MissionManager.css

@@ -215,8 +215,9 @@
 }
 
 .mission-manager__sidebar-cta {
-  flex: 1;
+  width: 100%;
   justify-content: center;
+  gap: var(--space-sm);
 }
 
 /* Hide duplicate sidebar title; the shared header already labels this view. */
@@ -318,6 +319,31 @@
   padding: var(--space-2xl) var(--space-xl);
 }
 
+.mission-manager__empty--mission {
+  gap: var(--space-md);
+  max-width: 420px;
+  margin: 0 auto;
+}
+
+.mission-manager__empty-title {
+  margin: 0;
+  font-size: 16px;
+  font-weight: 600;
+  color: var(--text);
+}
+
+.mission-manager__empty-body {
+  margin: 0;
+  font-size: 13px;
+  line-height: 1.5;
+  color: var(--text-muted);
+}
+
+.mission-manager__empty-cta {
+  margin-top: var(--space-sm);
+  gap: var(--space-sm);
+}
+
 /* ── Status Badge ── */
 /* Fine-grained badge paddings stay pixel-specific for compact legibility. */
 .mission-status-badge {
@@ -779,8 +805,9 @@
 }
 
 .mission-list__item-progress {
-  flex: 1;
+  width: 100%;
   height: 4px;
+  margin-top: var(--space-xs);
   background: var(--bg-tertiary);
   border-radius: 2px;
   overflow: hidden;