fire-planner: UX review pass 2 — health URL, Progress in shell, Gantt

single-year drag, Settings highlight, Dashboard empty state

Round 2 of agent-driven UX review.

- api status badge was always "unreachable" because client called
  /api/healthz but FastAPI mounts /healthz at root (so k8s probes
  hit it without the SPA prefix). Client now calls /healthz directly.
- Progress page rendered without the shell sidebar/tabs because its
  route was sibling to ScenarioShell; moved it inside as a nested
  route (also drops the redundant "← Plan" breadcrumb since the tab
  bar handles that now).
- EventGantt: single-year (point) events no longer render edge handles
  since the bar is too narrow to distinguish "edge grab" from "middle
  grab" — for points the whole bar moves; resize via the popover.
  Bars wider than 24px keep their edge handles.
- Settings sub-nav: Milestones now points at /settings/milestones
  (consistent active highlight); /settings index redirects there.
- Dashboard "Last 12 months" chart shows an explainer when the
  history has fewer than 2 snapshots instead of an empty axis.
- Stub tabs that are currently active get a slate-300 underline +
  slate-500 text rather than the bold slate-900 — visually honest
  about what's a placeholder.

Frontend typecheck/test/build green.

frontend/src/components/EventGantt.tsx

@@ -288,6 +288,12 @@ function Inner({
             const fill = CATEGORY_FILL[ev.category] ?? CATEGORY_FILL.essential;
             const border =
               CATEGORY_BORDER[ev.category] ?? CATEGORY_BORDER.essential;
+            // Edge handles are only useful on multi-year ranges. For
+            // single-year (point) events the bar is too narrow to
+            // distinguish "edge" from "middle" so the whole bar
+            // moves and the user resizes via the popover.
+            const showHandles = w >= 24 && yearEnd > ev.year_start;
+            const handleW = Math.min(8, w / 4);
             return (
               <g
                 key={ev.id}
@@ -306,28 +312,30 @@ function Inner({
                   rx={3}
                   onMouseDown={(e) => startDrag(e, ev, 'move')}
                 />
-                {/* Left handle */}
-                <rect
-                  x={x - 1}
-                  y={y}
-                  width={6}
-                  height={h}
-                  fill="rgba(0,0,0,0.25)"
-                  rx={3}
-                  onMouseDown={(e) => startDrag(e, ev, 'left')}
-                  style={{ cursor: 'ew-resize' }}
-                />
-                {/* Right handle */}
-                <rect
-                  x={x + w - 5}
-                  y={y}
-                  width={6}
-                  height={h}
-                  fill="rgba(0,0,0,0.25)"
-                  rx={3}
-                  onMouseDown={(e) => startDrag(e, ev, 'right')}
-                  style={{ cursor: 'ew-resize' }}
-                />
+                {showHandles && (
+                  <>
+                    <rect
+                      x={x - 1}
+                      y={y}
+                      width={handleW}
+                      height={h}
+                      fill="rgba(0,0,0,0.25)"
+                      rx={3}
+                      onMouseDown={(e) => startDrag(e, ev, 'left')}
+                      style={{ cursor: 'ew-resize' }}
+                    />
+                    <rect
+                      x={x + w - handleW + 1}
+                      y={y}
+                      width={handleW}
+                      height={h}
+                      fill="rgba(0,0,0,0.25)"
+                      rx={3}
+                      onMouseDown={(e) => startDrag(e, ev, 'right')}
+                      style={{ cursor: 'ew-resize' }}
+                    />
+                  </>
+                )}
                 <text
                   x={x + 6}
                   y={y + h / 2}