fix: Resolve all ESLint errors and warnings in web package

Fixes all 542 ESLint problems in the web package to achieve 0 errors and 0 warnings.

Changes:
- Fixed 144 issues: nullish coalescing, return types, unused variables
- Fixed 118 issues: unnecessary conditions, type safety, template literals
- Fixed 79 issues: non-null assertions, unsafe assignments, empty functions
- Fixed 67 issues: explicit return types, promise handling, enum comparisons
- Fixed 45 final warnings: missing return types, optional chains
- Fixed 25 typecheck-related issues: async/await, type assertions, formatting
- Fixed JSX.Element namespace errors across 90+ files

All Quality Rails violations resolved. Lint and typecheck both pass with 0 problems.

Files modified: 118 components, tests, hooks, and utilities

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/components/knowledge/EntryGraphViewer.tsx

@@ -41,7 +41,10 @@ interface EntryGraphViewerProps {
   initialDepth?: number;
 }
 
-export function EntryGraphViewer({ slug, initialDepth = 1 }: EntryGraphViewerProps) {
+export function EntryGraphViewer({
+  slug,
+  initialDepth = 1,
+}: EntryGraphViewerProps): React.JSX.Element {
   const [graphData, setGraphData] = useState<EntryGraphResponse | null>(null);
   const [depth, setDepth] = useState(initialDepth);
   const [isLoading, setIsLoading] = useState(true);
@@ -65,7 +68,7 @@ export function EntryGraphViewer({ slug, initialDepth = 1 }: EntryGraphViewerPro
     void loadGraph();
   }, [loadGraph]);
 
-  const handleDepthChange = (newDepth: number) => {
+  const handleDepthChange = (newDepth: number): void => {
     setDepth(newDepth);
   };
 
@@ -77,7 +80,7 @@ export function EntryGraphViewer({ slug, initialDepth = 1 }: EntryGraphViewerPro
     );
   }
 
-  if (error || !graphData) {
+  if (error ?? !graphData) {
     return (
       <div className="p-8 text-center">
         <div className="text-red-500 mb-2">Error loading graph</div>
@@ -91,7 +94,7 @@ export function EntryGraphViewer({ slug, initialDepth = 1 }: EntryGraphViewerPro
   // Group nodes by depth for better visualization
   const nodesByDepth = nodes.reduce<Record<number, GraphNode[]>>((acc, node) => {
     const d = node.depth;
-    if (!acc[d]) acc[d] = [];
+    acc[d] ??= [];
     acc[d].push(node);
     return acc;
   }, {});
@@ -194,7 +197,7 @@ export function EntryGraphViewer({ slug, initialDepth = 1 }: EntryGraphViewerPro
                       key={tag.id}
                       className="inline-flex items-center px-2.5 py-0.5 rounded text-xs font-medium"
                       style={{
-                        backgroundColor: tag.color || "#6B7280",
+                        backgroundColor: tag.color ?? "#6B7280",
                         color: "#FFFFFF",
                       }}
                     >
@@ -242,7 +245,13 @@ interface NodeCardProps {
   connections?: { incoming: number; outgoing: number };
 }
 
-function NodeCard({ node, isCenter, onClick, isSelected, connections }: NodeCardProps) {
+function NodeCard({
+  node,
+  isCenter,
+  onClick,
+  isSelected,
+  connections,
+}: NodeCardProps): React.JSX.Element {
   return (
     <div
       onClick={onClick}
@@ -269,7 +278,7 @@ function NodeCard({ node, isCenter, onClick, isSelected, connections }: NodeCard
                   key={tag.id}
                   className="inline-flex items-center px-2 py-0.5 rounded text-xs font-medium"
                   style={{
-                    backgroundColor: tag.color || "#6B7280",
+                    backgroundColor: tag.color ?? "#6B7280",
                     color: "#FFFFFF",
                   }}
                 >
@@ -294,7 +303,10 @@ function NodeCard({ node, isCenter, onClick, isSelected, connections }: NodeCard
   );
 }
 
-function getNodeConnections(nodeId: string, edges: GraphEdge[]) {
+function getNodeConnections(
+  nodeId: string,
+  edges: GraphEdge[]
+): { incoming: number; outgoing: number } {
   const incoming = edges.filter((e) => e.targetId === nodeId).length;
   const outgoing = edges.filter((e) => e.sourceId === nodeId).length;
   return { incoming, outgoing };