test(worker): consolidate fakes into Infrastructure/, drop tag-era names

- Extract FakeClaudeProcess to Infrastructure/FakeClaudeProcess.cs (was
  defined inline in QueueServiceTests #region); all consumers updated
- Replace duplicate FakeHubContext/FakeHubClients/FakeClientProxy
  (QueueServiceTests) with existing CapturingHubContext from Infrastructure
  across all 7 affected files; Planning's file-local FakeHubContext kept
- Rename SeedListWithAgentTag → SeedListAsync (return Task<string>, drop
  unused agentTagId tuple element) and SeedListWithAgentTagAsync → SeedListAsync
- PrimeRunnerTests keeps its private nested FakeClaudeProcess: constructor
  API (delay/exitCode/lines/result params) differs from the shared one and
  replacement would require rewriting every test in that file

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

tests/ClaudeDo.Worker.Tests/Infrastructure/FakeClaudeProcess.cs

@@ -0,0 +1,25 @@
+using ClaudeDo.Worker.Runner;
+
+namespace ClaudeDo.Worker.Tests.Infrastructure;
+
+internal sealed class FakeClaudeProcess : IClaudeProcess
+{
+    private readonly Func<string, string, IReadOnlyList<string>, Func<string, Task>, CancellationToken, Task<RunResult>> _handler;
+    private int _callCount;
+
+    public int CallCount => _callCount;
+
+    public FakeClaudeProcess(
+        Func<string, string, IReadOnlyList<string>, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
+    {
+        _handler = handler ?? ((_, _, _, _, _) =>
+            Task.FromResult(new RunResult { ExitCode = 0, ResultMarkdown = "ok" }));
+    }
+
+    public async Task<RunResult> RunAsync(IReadOnlyList<string> arguments, string prompt, string workingDirectory,
+        Func<string, Task> onStdoutLine, CancellationToken ct)
+    {
+        Interlocked.Increment(ref _callCount);
+        return await _handler(prompt, workingDirectory, arguments, onStdoutLine, ct);
+    }
+}