fix: Resolve web package lint and typecheck errors

Fixes ESLint and TypeScript errors in web package to pass CI checks:

- Fixed all Quality Rails violations (14 explicit any types)
- Fixed deprecated React event types (FormEvent → SyntheticEvent)
- Fixed 26 TypeScript errors (Promise types, test mocks, HTMLElement assertions)
- Added vitest DOM matcher type definitions
- Fixed unused variables and empty functions
- Resolved 43+ additional lint errors

Typecheck: ✅ 0 errors
Lint: 542 remaining (non-blocking in CI)

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

apps/web/src/app/(authenticated)/knowledge/[slug]/page.tsx

@@ -256,7 +256,13 @@ export default function EntryPage(): ReactElement {
   }
 
   if (!entry) {
-    return null;
+    return (
+      <div className="max-w-4xl mx-auto p-6">
+        <div className="p-4 bg-gray-50 dark:bg-gray-900/20 border border-gray-200 dark:border-gray-800 rounded-md">
+          <p className="text-sm text-gray-800 dark:text-gray-200">Entry not found</p>
+        </div>
+      </div>
+    );
   }
 
   return (

apps/web/src/app/(authenticated)/knowledge/new/page.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import type { ReactElement, FormEvent as ReactFormEvent } from "react";
+import type { ReactElement } from "react";
 import React, { useState, useEffect, useCallback } from "react";
 import { useRouter } from "next/navigation";
 import { EntryStatus, Visibility, type KnowledgeTag } from "@mosaic/shared";
@@ -107,7 +107,7 @@ export default function NewEntryPage(): ReactElement {
     }
   };
 
-  const handleSubmit = (e: ReactFormEvent): void => {
+  const handleSubmit = (e: React.SyntheticEvent<HTMLFormElement>): void => {
     e.preventDefault();
     void handleSave();
   };