feat(worker): add DefaultAgentSeeder for first-launch agent seeding

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Worker/Services/DefaultAgentSeeder.cs

@@ -0,0 +1,60 @@
+using Microsoft.Extensions.Logging;
+
+namespace ClaudeDo.Worker.Services;
+
+public sealed record SeedResult(int Copied, int Skipped);
+
+public sealed class DefaultAgentSeeder
+{
+    private readonly string _bundleDir;
+    private readonly string _targetDir;
+    private readonly ILogger<DefaultAgentSeeder>? _logger;
+
+    public DefaultAgentSeeder(string bundleDir, string targetDir, ILogger<DefaultAgentSeeder>? logger = null)
+    {
+        _bundleDir = bundleDir;
+        _targetDir = targetDir;
+        _logger = logger;
+    }
+
+    public async Task<SeedResult> SeedMissingAsync(CancellationToken ct = default)
+    {
+        if (!Directory.Exists(_bundleDir))
+        {
+            _logger?.LogWarning("DefaultAgents bundle dir not found: {Dir}", _bundleDir);
+            return new SeedResult(0, 0);
+        }
+
+        Directory.CreateDirectory(_targetDir);
+
+        int copied = 0;
+        int skipped = 0;
+
+        foreach (var src in Directory.EnumerateFiles(_bundleDir, "*.md"))
+        {
+            ct.ThrowIfCancellationRequested();
+            var fileName = Path.GetFileName(src);
+            var dst = Path.Combine(_targetDir, fileName);
+
+            if (File.Exists(dst))
+            {
+                skipped++;
+                continue;
+            }
+
+            try
+            {
+                using var input = File.OpenRead(src);
+                using var output = File.Create(dst);
+                await input.CopyToAsync(output, ct);
+                copied++;
+            }
+            catch (Exception ex)
+            {
+                _logger?.LogWarning(ex, "Failed to copy default agent {File}", fileName);
+            }
+        }
+
+        return new SeedResult(copied, skipped);
+    }
+}