feat(rate-limiting): Implement core rate limiting functionality with configuration, decision-making, metrics, middleware, and service registration

- Add RateLimitConfig for configuration management with YAML binding support.
- Introduce RateLimitDecision to encapsulate the result of rate limit checks.
- Implement RateLimitMetrics for OpenTelemetry metrics tracking.
- Create RateLimitMiddleware for enforcing rate limits on incoming requests.
- Develop RateLimitService to orchestrate instance and environment rate limit checks.
- Add RateLimitServiceCollectionExtensions for dependency injection registration.

docs/modules/taskrunner/architecture.md

@@ -12,7 +12,7 @@
 - **WebService** (`StellaOps.TaskRunner.WebService`) - HTTP API, plan hash validation, SSE log streaming, approval endpoints.
 - **Worker** (`StellaOps.TaskRunner.Worker`) - run orchestration, retries/backoff, artifact capture, attestation generation.
 - **Core** (`StellaOps.TaskRunner.Core`) - execution graph builder, simulation engine, step state machine, policy/approval gate abstractions.
-- **Infrastructure** (`StellaOps.TaskRunner.Infrastructure`) - storage adapters (Mongo, file), artifact/object store clients, evidence bundle writer.
+- **Infrastructure** (`StellaOps.TaskRunner.Infrastructure`) - storage adapters (PostgreSQL, file), artifact/object store clients, evidence bundle writer.
 
 ## 3. Execution Phases
 1. **Plan** - parse manifest, validate schema, resolve inputs/secrets, build execution graph, compute canonical `planHash` (SHA-256 over normalised graph).
@@ -29,7 +29,7 @@
 - `POST /api/runs/{runId}/cancel` (`packs.run`) - cancel active run.
 - TODO (Phase II): `GET /.well-known/openapi` (TASKRUN-OAS-61-002) after OAS publication.
 
-## 5. Data Model (Mongo, mirrors migration doc)
+## 5. Data Model (PostgreSQL, mirrors migration doc)
 - **pack_runs**: `_id`, `planHash`, `plan`, `failurePolicy`, `requestedAt`, `createdAt`, `updatedAt`, `steps[]`, `tenantId`.
 - **pack_run_logs**: `_id`, `runId`, `sequence` (monotonic), `timestamp` (UTC), `level`, `eventType`, `message`, `stepId?`, `metadata`.
 - **pack_artifacts**: `_id`, `runId`, `name`, `type`, `sourcePath?`, `storedPath?`, `status`, `notes?`, `capturedAt`.
@@ -65,18 +65,17 @@
 - **Export Center** - evidence bundles and manifests for offline/air-gapped export.
 - **Orchestrator/CLI** - submission + resume flows; SSE log consumption.
 
-## 11. Configuration (Mongo example)
+## 11. Configuration (PostgreSQL example)
 ```json
 \"TaskRunner\": {
   \"Storage\": {
-    \"Mode\": \"mongo\",
-    \"Mongo\": {
-      \"ConnectionString\": \"mongodb://127.0.0.1:27017/taskrunner\",
-      \"Database\": \"taskrunner\",
-      \"RunsCollection\": \"pack_runs\",
-      \"LogsCollection\": \"pack_run_logs\",
-      \"ArtifactsCollection\": \"pack_artifacts\",
-      \"ApprovalsCollection\": \"pack_run_approvals\"
+    \"Mode\": \"postgresql\",
+    \"PostgreSQL\": {
+      \"ConnectionString\": \"Host=127.0.0.1;Database=taskrunner;Username=stellaops;Password=secret\",
+      \"RunsTable\": \"pack_runs\",
+      \"LogsTable\": \"pack_run_logs\",
+      \"ArtifactsTable\": \"pack_artifacts\",
+      \"ApprovalsTable\": \"pack_run_approvals\"
     }
   }
 }