feat: Add Go module and workspace test fixtures

- Created expected JSON files for Go modules and workspaces.
- Added go.mod and go.sum files for example projects.
- Implemented private module structure with expected JSON output.
- Introduced vendored dependencies with corresponding expected JSON.
- Developed PostgresGraphJobStore for managing graph jobs.
- Established SQL migration scripts for graph jobs schema.
- Implemented GraphJobRepository for CRUD operations on graph jobs.
- Created IGraphJobRepository interface for repository abstraction.
- Added unit tests for GraphJobRepository to ensure functionality.

src/Scheduler/StellaOps.Scheduler.WebService/GraphJobs/PostgresGraphJobStore.cs

@@ -0,0 +1,82 @@
+using System.Collections.Generic;
+using StellaOps.Scheduler.Models;
+using StellaOps.Scheduler.Storage.Postgres.Repositories;
+
+namespace StellaOps.Scheduler.WebService.GraphJobs;
+
+internal sealed class PostgresGraphJobStore : IGraphJobStore
+{
+    private readonly IGraphJobRepository _repository;
+
+    public PostgresGraphJobStore(IGraphJobRepository repository)
+    {
+        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
+    }
+
+    public async ValueTask<GraphBuildJob> AddAsync(GraphBuildJob job, CancellationToken cancellationToken)
+    {
+        await _repository.InsertAsync(job, cancellationToken);
+        return job;
+    }
+
+    public async ValueTask<GraphOverlayJob> AddAsync(GraphOverlayJob job, CancellationToken cancellationToken)
+    {
+        await _repository.InsertAsync(job, cancellationToken);
+        return job;
+    }
+
+    public async ValueTask<GraphJobCollection> GetJobsAsync(string tenantId, GraphJobQuery query, CancellationToken cancellationToken)
+    {
+        var normalized = query.Normalize();
+        var builds = normalized.Type is null or GraphJobQueryType.Build
+            ? await _repository.ListBuildJobsAsync(tenantId, normalized.Status, normalized.Limit ?? 50, cancellationToken)
+            : Array.Empty<GraphBuildJob>();
+
+        var overlays = normalized.Type is null or GraphJobQueryType.Overlay
+            ? await _repository.ListOverlayJobsAsync(tenantId, normalized.Status, normalized.Limit ?? 50, cancellationToken)
+            : Array.Empty<GraphOverlayJob>();
+
+        return GraphJobCollection.From(builds, overlays);
+    }
+
+    public async ValueTask<GraphBuildJob?> GetBuildJobAsync(string tenantId, string jobId, CancellationToken cancellationToken)
+        => await _repository.GetBuildJobAsync(tenantId, jobId, cancellationToken);
+
+    public async ValueTask<GraphOverlayJob?> GetOverlayJobAsync(string tenantId, string jobId, CancellationToken cancellationToken)
+        => await _repository.GetOverlayJobAsync(tenantId, jobId, cancellationToken);
+
+    public async ValueTask<GraphJobUpdateResult<GraphBuildJob>> UpdateAsync(GraphBuildJob job, GraphJobStatus expectedStatus, CancellationToken cancellationToken)
+    {
+        if (await _repository.TryReplaceAsync(job, expectedStatus, cancellationToken).ConfigureAwait(false))
+        {
+            return GraphJobUpdateResult<GraphBuildJob>.UpdatedResult(job);
+        }
+
+        var existing = await _repository.GetBuildJobAsync(job.TenantId, job.Id, cancellationToken).ConfigureAwait(false);
+        if (existing is null)
+        {
+            throw new KeyNotFoundException($"Graph build job '{job.Id}' not found.");
+        }
+
+        return GraphJobUpdateResult<GraphBuildJob>.NotUpdated(existing);
+    }
+
+    public async ValueTask<GraphJobUpdateResult<GraphOverlayJob>> UpdateAsync(GraphOverlayJob job, GraphJobStatus expectedStatus, CancellationToken cancellationToken)
+    {
+        if (await _repository.TryReplaceOverlayAsync(job, expectedStatus, cancellationToken).ConfigureAwait(false))
+        {
+            return GraphJobUpdateResult<GraphOverlayJob>.UpdatedResult(job);
+        }
+
+        var existing = await _repository.GetOverlayJobAsync(job.TenantId, job.Id, cancellationToken).ConfigureAwait(false);
+        if (existing is null)
+        {
+            throw new KeyNotFoundException($"Graph overlay job '{job.Id}' not found.");
+        }
+
+        return GraphJobUpdateResult<GraphOverlayJob>.NotUpdated(existing);
+    }
+
+    public async ValueTask<IReadOnlyCollection<GraphOverlayJob>> GetOverlayJobsAsync(string tenantId, CancellationToken cancellationToken)
+        => await _repository.ListOverlayJobsAsync(tenantId, cancellationToken);
+}