feat: rebuild Experiments tab with Difference-in-Differences analysis and Bayesian verdicts

Replace the basic CRUD experiment tracker with a scientifically rigorous A/B testing system:

- Add DiD analysis engine (services/experimentAnalysis.ts) that computes treatment vs control
  group comparisons across 7 metrics (units, sessions, CVR, CTR, ROAS, revenue, ACOS)
- Implement Bayesian verdict system (Winner/Loser/Inconclusive) using posterior probability
  with normal CDF approximation (Abramowitz & Stegun erf, no external deps)
- Build counterfactual time series for trend charts (actual vs estimated without change)
- Rewrite ExperimentsView as single component with 3 inline sub-views (list, detail, create)
  replacing the previous modal-based ExperimentDetail and ExperimentForm
- Add control group support, change annotations (before→after diffs), and SEO experiment type
- New types: ExperimentChangeAnnotation, DiDMetricResult, DifferenceInDifferencesResult,
  ExperimentVerdict
- Simplify App.tsx by removing experiment modal state (5 useState hooks eliminated)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

App.tsx

@@ -23,8 +23,7 @@ const AdsPerformance = lazy(() => import('./components/AdsPerformance'));
 const ForecastView = lazy(() => import('./components/ForecastView'));
 const VendorDataView = lazy(() => import('./components/VendorDataView'));
 const ExperimentsView = lazy(() => import('./components/ExperimentsView'));
-const ExperimentDetail = lazy(() => import('./components/ExperimentDetail'));
-const ExperimentForm = lazy(() => import('./components/ExperimentForm'));
+// ExperimentDetail and ExperimentForm are now integrated into ExperimentsView
 
 // Loading fallback component
 const LoadingSpinner = () => (
@@ -64,17 +63,7 @@ const App: React.FC = () => {
 
   // Experiments state
   const [experimentMap, setExperimentMap] = useState<Map<string, ActiveExperiment[]>>(new Map());
-  const [selectedExperimentId, setSelectedExperimentId] = useState<string | null>(null);
-  const [showCreateExperiment, setShowCreateExperiment] = useState(false);
-  const [preselectedAsins, setPreselectedAsins] = useState<string[]>([]);
-  const [preselectedMarketplace, setPreselectedMarketplace] = useState<string>('');
-  const [preselectedLine, setPreselectedLine] = useState<string>('');
-
-  // Available product lines (for experiment form)
-  const availableProductLines = useMemo(() => {
-    const lines = new Set(rawData.map(r => r.line).filter(Boolean));
-    return Array.from(lines).sort();
-  }, [rawData]);
+  // Experiment modal state removed — detail/create are now inline in ExperimentsView
 
   // Modal State
   const [isDataModalOpen, setIsDataModalOpen] = useState(false);
@@ -349,13 +338,10 @@ const App: React.FC = () => {
     setView('ads');
   }, []);
 
-  // Create experiment for a specific line
-  const handleCreateExperimentForLine = useCallback((line: string) => {
-    if (!line) return;
-    setPreselectedLine(line);
-    setPreselectedMarketplace(filters.customer[0] || '');
-    setShowCreateExperiment(true);
-  }, [filters.customer]);
+  // Create experiment for a specific line — now handled inline by ExperimentsView
+  const handleCreateExperimentForLine = useCallback((_line: string) => {
+    setView('experiments');
+  }, []);
 
   // 1. Initial Load from Cache (IndexedDB) or Auto-Fetch Permanent URL
   useEffect(() => {
@@ -902,7 +888,7 @@ const App: React.FC = () => {
                     velocityMap={velocityMap}
                     buyBoxLostMap={buyBoxLostMap}
                     experimentMap={experimentMap}
-                    onOpenExperiment={(id) => setSelectedExperimentId(id)}
+                    onOpenExperiment={() => setView('experiments')}
                   />
                 </div>
               </Suspense>
@@ -962,13 +948,8 @@ const App: React.FC = () => {
               <Suspense fallback={<LoadingSpinner />}>
                 <div className={view === 'experiments' ? '' : 'hidden'}>
                   <ExperimentsView
-                    onOpenDetail={(id) => setSelectedExperimentId(id)}
-                    onOpenCreate={() => {
-                      setPreselectedAsins([]);
-                      setPreselectedMarketplace(filters.customer[0] || '');
-                      setShowCreateExperiment(true);
-                    }}
                     salesData={unfilteredCombinedData}
+                    onExperimentsFetch={handleExperimentsFetch}
                   />
                 </div>
               </Suspense>
@@ -1036,33 +1017,7 @@ const App: React.FC = () => {
         )
       }
 
-      {/* Experiment Detail Modal */}
-      {selectedExperimentId && (
-        <ExperimentDetail
-          experimentId={selectedExperimentId}
-          onClose={() => setSelectedExperimentId(null)}
-          salesData={unfilteredCombinedData}
-        />
-      )}
-
-      {/* Create Experiment Modal */}
-      {showCreateExperiment && (
-        <ExperimentForm
-          onClose={() => {
-            setShowCreateExperiment(false);
-            setPreselectedAsins([]);
-            setPreselectedMarketplace('');
-            setPreselectedLine('');
-          }}
-          onSuccess={() => {
-            handleExperimentsFetch();
-          }}
-          initialAsins={preselectedAsins}
-          initialMarketplace={preselectedMarketplace}
-          initialLine={preselectedLine}
-          availableLines={availableProductLines}
-        />
-      )}
+      {/* Experiment modals removed — detail/create are now inline in ExperimentsView */}
 
     </div >
   );