Add UK education verification and security fixes

Features:
- Add UK institution recognition (170+ universities)
- Add diploma mill detection (100+ blacklisted institutions)
- Add education verification service with date plausibility checks
- Add local file storage option (no Azure required)
- Add default admin user seeding on startup
- Enhance Serilog logging with file output

Security fixes:
- Fix path traversal vulnerability in LocalFileStorageService
- Fix open redirect in login endpoint (use LocalRedirect)
- Fix password validation message (12 chars, not 6)
- Fix login to use HTTP POST endpoint (avoid Blazor cookie issues)

Code improvements:
- Add CancellationToken propagation to CV parser
- Add shared helpers (JsonDefaults, DateHelpers, ScoreThresholds)
- Add IUserContextService for user ID extraction
- Parallelized company verification in ProcessCVCheckJob
- Add 28 unit tests for education verification

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

src/TrueCV.Infrastructure/Services/UserContextService.cs

@@ -0,0 +1,28 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Components.Authorization;
+using TrueCV.Application.Interfaces;
+
+namespace TrueCV.Infrastructure.Services;
+
+public sealed class UserContextService : IUserContextService
+{
+    private readonly AuthenticationStateProvider _authenticationStateProvider;
+
+    public UserContextService(AuthenticationStateProvider authenticationStateProvider)
+    {
+        _authenticationStateProvider = authenticationStateProvider;
+    }
+
+    public async Task<Guid?> GetCurrentUserIdAsync()
+    {
+        var authState = await _authenticationStateProvider.GetAuthenticationStateAsync();
+        var userIdClaim = authState.User.FindFirst(ClaimTypes.NameIdentifier)?.Value;
+
+        if (string.IsNullOrEmpty(userIdClaim) || !Guid.TryParse(userIdClaim, out var userId))
+        {
+            return null;
+        }
+
+        return userId;
+    }
+}