M4: agent-run job queue + worker drain (Increment 1)

SharedKernel: IWorkerModule seam (RegisterWorker runs in the worker host only).
Bootstrap: AddTeamUpWorkerServices; the worker host now wires it.

Assembler module (schema "assembler", InitialAssembler migration):
- Job (Pending→Processing→Done/Failed) + AgentRun (Queued→Running→Completed/Failed) entities.
- JobQueue: enqueue + ClaimNextAsync using `FOR UPDATE SKIP LOCKED` in a transaction.
- AgentRunExecutor (Increment-1 placeholder — real assemble/model/parse lands in Increment 2).
- JobProcessor BackgroundService drains the queue on the worker host (web off the model path).
- POST /api/assembler/runs enqueues a run; GET /api/assembler/runs/{id} reads it.

Verified: build green; ArchitectureTests 8/8 (Assembler references only SharedKernel);
IntegrationTests 28/28 incl. enqueue→claim(SKIP LOCKED)→process→Completed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Modules/TeamUp.Modules.Assembler/Runtime/AgentRunExecutor.cs

@@ -0,0 +1,48 @@
+using System.Text.Json;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using TeamUp.Modules.Assembler.Domain;
+using TeamUp.Modules.Assembler.Persistence;
+
+namespace TeamUp.Modules.Assembler.Runtime;
+
+internal sealed record AgentRunPayload(Guid RunId);
+
+/// <summary>
+/// Processes one claimed job: drives the AgentRun lifecycle. In M4 Increment 1 it records a
+/// placeholder; Increment 2 swaps the middle for the real assembler (assemble → model → parse).
+/// </summary>
+internal sealed class AgentRunExecutor(AssemblerDbContext db, TimeProvider clock, ILogger<AgentRunExecutor> logger)
+{
+    public async Task ProcessAsync(Job job, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var payload = JsonSerializer.Deserialize<AgentRunPayload>(job.Payload)
+                ?? throw new InvalidOperationException("Invalid job payload.");
+
+            var run = await db.AgentRuns.FirstOrDefaultAsync(r => r.Id == payload.RunId, cancellationToken)
+                ?? throw new InvalidOperationException($"AgentRun {payload.RunId} not found.");
+
+            run.Start(agentId: null, prompt: "[assembler pending — M4 Increment 2]", trace: null);
+            await db.SaveChangesAsync(cancellationToken);
+
+            // TODO (M4 Increment 2): assemble the prompt, call the model, parse into action + risk.
+            run.Complete(
+                output: "[assembler pending]",
+                actionType: "pending",
+                actionRisk: "read",
+                resultJson: null,
+                latencyMs: 0,
+                clock.GetUtcNow());
+            job.MarkDone(clock.GetUtcNow());
+            await db.SaveChangesAsync(cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            job.MarkFailed(ex.Message, clock.GetUtcNow());
+            await db.SaveChangesAsync(cancellationToken);
+            logger.LogError(ex, "Agent-run job {JobId} failed.", job.Id);
+        }
+    }
+}