Add integration tests for Proof Chain and Reachability workflows

- Implement ProofChainTestFixture for PostgreSQL-backed integration tests.
- Create StellaOps.Integration.ProofChain project with necessary dependencies.
- Add ReachabilityIntegrationTests to validate call graph extraction and reachability analysis.
- Introduce ReachabilityTestFixture for managing corpus and fixture paths.
- Establish StellaOps.Integration.Reachability project with required references.
- Develop UnknownsWorkflowTests to cover the unknowns lifecycle: detection, ranking, escalation, and resolution.
- Create StellaOps.Integration.Unknowns project with dependencies for unknowns workflow.

src/Scanner/StellaOps.Scanner.WebService/Security/AnonymousAuthenticationHandler.cs

@@ -6,6 +6,10 @@ using Microsoft.Extensions.Options;
 
 namespace StellaOps.Scanner.WebService.Security;
 
+/// <summary>
+/// Authentication handler for anonymous/development mode that creates
+/// a synthetic user identity for testing and local development.
+/// </summary>
 internal sealed class AnonymousAuthenticationHandler : AuthenticationHandler<AuthenticationSchemeOptions>
 {
     public AnonymousAuthenticationHandler(
@@ -18,9 +22,18 @@ internal sealed class AnonymousAuthenticationHandler : AuthenticationHandler<Aut
 
     protected override Task<AuthenticateResult> HandleAuthenticateAsync()
     {
-        var identity = new ClaimsIdentity(authenticationType: Scheme.Name);
+        // Create identity with standard claims that endpoints may require
+        var claims = new[]
+        {
+            new Claim(ClaimTypes.NameIdentifier, "anonymous-user"),
+            new Claim(ClaimTypes.Name, "Anonymous User"),
+            new Claim(ClaimTypes.Email, "anonymous@localhost"),
+            new Claim("sub", "anonymous-user"),
+        };
+
+        var identity = new ClaimsIdentity(claims, authenticationType: Scheme.Name);
         var principal = new ClaimsPrincipal(identity);
         var ticket = new AuthenticationTicket(principal, Scheme.Name);
         return Task.FromResult(AuthenticateResult.Success(ticket));
     }
-}
+}