feat(ui/alerts): rule editor wizard shell + form-state module

Wizard navigates 5 steps (scope/condition/trigger/notify/review) with
per-step validation. form-state module is the single source of truth for
the rule form; initialForm/toRequest/validateStep are unit-tested (6
tests). Step components are stubbed and will be implemented in Tasks
20-24. prefillFromPromotion is a thin wrapper in this commit; Task 24
rewrites it to compute scope-adjustment warnings.

Deviation notes:
 - FormState.targets uses {kind, targetId} to match AlertRuleTarget DTO
   field names (plan draft had targetKind).
 - toRequest casts through Record<string, unknown> so the spread over
   the Partial<AlertCondition> union typechecks.

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

ui/src/pages/Alerts/RuleEditor/wizard.module.css

@@ -0,0 +1,57 @@
+.wizard {
+  padding: 16px;
+  display: flex;
+  flex-direction: column;
+  gap: 16px;
+}
+
+.header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  gap: 12px;
+  flex-wrap: wrap;
+}
+
+.promoteBanner {
+  padding: 8px 12px;
+  background: var(--amber-bg, rgba(255, 180, 0, 0.12));
+  border: 1px solid var(--amber);
+  border-radius: 6px;
+  font-size: 13px;
+}
+
+.steps {
+  display: flex;
+  gap: 8px;
+  border-bottom: 1px solid var(--border);
+  padding-bottom: 8px;
+}
+
+.step {
+  background: none;
+  border: none;
+  padding: 8px 12px;
+  border-bottom: 2px solid transparent;
+  cursor: pointer;
+  color: var(--muted);
+  font-size: 13px;
+}
+
+.stepActive {
+  color: var(--fg);
+  border-bottom-color: var(--accent);
+}
+
+.stepDone {
+  color: var(--fg);
+}
+
+.stepBody {
+  min-height: 320px;
+}
+
+.footer {
+  display: flex;
+  justify-content: space-between;
+}