feat(JwtBearer): SafeWebCore.JwtBearer module - fail-fast/loud broken JWT authority + hardening

[MPCoreDeveloper]

SafeWebCore.JwtBearer

Optional companion module for SafeWebCore that makes a misconfigured or unreachable JWT authority fail loud before your users ever see a 401, plus optional token hardening.

Why

Fixes the exact scenario from dotnet/aspnetcore#67991 (reported by Stephan van Rooij / @svrooij, milestone .NET 12 Planning): a misspelled authority (\organisations\ vs \organizations) lets the app start normally while every request 401s silently.

What this adds

• \JwtAuthorityValidationGuard\ (IHostedService): eagerly loads the OpenID Connect metadata at startup; HTTP 4xx = permanent -> Error log + optional fail-fast; transient = Warning, app starts.
• \AddJwtBearerAuthorityValidation(...), \AddJwtBearerHardening(...), and the one-liner \AddSafeWebCoreJwtBearer(...).
• Token hardening (opt-in): signed tokens (\�lg: none\ rejected), algorithm allow-list, typ-header checks, audience/issuer enforcement, max clock skew / token lifetime, jti/nbf/iat.
• Runtime metadata logging: decorator around \IConfigurationManager\ (IdentityModel 8.19.2) logs metadata failures at Error/Warning during runtime.
• Stephan's repro as test AND example: \ ests/.../StephanReproIntegrationTests.cs\ (fake HTTP, deterministic) + runnable \�xamples/JwtBearerDemo/\ (broken vs fixed).

Verification

• \dotnet build SafeWebCore.slnx -c Release\ - clean (0 warnings, 0 errors)
• \dotnet test SafeWebCore.slnx -c Release\ - 163/163 passed (incl. 33 new JwtBearer tests)
• NuGet pack verified: README + icon + xml in \SafeWebCore.JwtBearer.1.0.0.nupkg\

SonarCloud

Waiting for the SonarCloud analysis on this PR (project \MPCoreDeveloper_SafeWebCore) - fixes will be applied until the Quality Gate is green, then this PR can be merged to master.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud