Doctor plugin checks: implement health check classes and documentation

Implement remediation-aware health checks across all Doctor plugin modules
(Agent, Attestor, Auth, BinaryAnalysis, Compliance, Crypto, Environment,
EvidenceLocker, Notify, Observability, Operations, Policy, Postgres, Release,
Scanner, Storage, Vex) and their backing library counterparts (AI, Attestation,
Authority, Core, Cryptography, Database, Docker, Integration, Notify,
Observability, Security, ServiceGraph, Sources, Verification).

Each check now emits structured remediation metadata (severity, category,
runbook links, and fix suggestions) consumed by the Doctor dashboard
remediation panel.

Also adds:
- docs/doctor/articles/ knowledge base for check explanations
- Advisory AI search seed and allowlist updates for doctor content
- Sprint plan for doctor checks documentation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/__Libraries/StellaOps.Doctor.Plugins.Cryptography/Checks/SmProviderCheck.cs

@@ -93,7 +93,8 @@ public sealed class SmProviderCheck : IDoctorCheck
                 .WithCauses(issues.ToArray())
                 .WithRemediation(r => r
                     .AddManualStep(1, "Set environment gate", "Set SM_SOFT_ALLOWED=1 to enable SM software providers")
-                    .AddManualStep(2, "Configure SmRemote", "Configure SmRemote:Endpoint for remote SM crypto service"))
+                    .AddManualStep(2, "Configure SmRemote", "Configure SmRemote:Endpoint for remote SM crypto service")
+                    .WithRunbookUrl("docs/doctor/articles/crypto/crypto-sm.md"))
                 .WithVerification("stella doctor --check check.crypto.sm")
                 .Build());
         }