Fix cache bypassing temporal company matching

- Cache lookup now validates company existed at claimed start date
- If cached company was incorporated after employment date, search for alternatives
- Fixes matching wrong company when cached data points to newer company

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

src/TrueCV.Infrastructure/Services/CompanyVerifierService.cs

@@ -51,12 +51,24 @@ public sealed class CompanyVerifierService : ICompanyVerifierService
         _logger.LogDebug("Verifying company: {CompanyName}", companyName);
         var flags = new List<CompanyVerificationFlag>();
 
-        // Try to find a cached match first
+        // Try to find a cached match first (but only if it existed at claimed start date)
         var cachedMatch = await FindCachedMatchAsync(companyName);
         if (cachedMatch is not null)
         {
-            _logger.LogDebug("Found cached company match for: {CompanyName}", companyName);
-            return CreateResultFromCache(cachedMatch, companyName, startDate, endDate, jobTitle, flags);
+            // Check if cached company existed at the claimed start date
+            var cacheValid = !startDate.HasValue ||
+                             cachedMatch.IncorporationDate == null ||
+                             cachedMatch.IncorporationDate <= startDate.Value;
+
+            if (cacheValid)
+            {
+                _logger.LogDebug("Found cached company match for: {CompanyName}", companyName);
+                return CreateResultFromCache(cachedMatch, companyName, startDate, endDate, jobTitle, flags);
+            }
+            else
+            {
+                _logger.LogDebug("Cached company {CachedName} was incorporated after claimed start date, searching for alternatives", cachedMatch.CompanyName);
+            }
         }
 
         // Search Companies House