M5: action gate + review inbox — edit distance captured for real

SharedKernel:
- ActionRisk (risk lives on the action) + GatePolicy (the pure autonomy x risk matrix:
  Read never holds, Draft/Publish hold unless Autonomous, Destructive ALWAYS holds).
- IActionGate (AgentActionProposal -> execute|hold) and IBoardWriter.AttachArtifactAsync.

Governance:
- ReviewItem (held action: artifact, child titles, trace, decision, edit distance) in a new
  review_items table (AddReviewItems migration).
- ActionGate: hold -> ReviewItem + "action.held" audit; autonomous -> execute + audit.
- HeldActionExecutor: writes the artifact onto the task and creates the child tasks via
  IBoardWriter (implemented by OrgBoard — no cross-module table access).
- Review inbox API: GET /api/governance/reviews (scope-filtered to where the caller may
  approve), POST /reviews/{id}/approve (optional edited content/children -> normalized
  edit distance recorded — the north-star metric), POST /reviews/{id}/sendback. Deciding
  twice is 409; Members are 403.

Assembler:
- OutputParser (numbered-list child titles, conservative) and the executor now hands every
  completed run's proposal to the gate.

OrgBoard: WorkItem.AttachArtifact + BoardWriter.AttachArtifactAsync.

Verified: build green; ArchitectureTests 8/8; IntegrationTests 41/41 incl. the full M5
acceptance — Aria (gated) proposes a spec, it waits in the inbox with its trace, a Member is
403'd, the owner edits-and-approves, the spec + four child stories land on the board, edit
distance > 0 is recorded and audited; Quill (autonomous) executes straight to the board;
destructive holds even for an autonomous seat and can be sent back. Plus the GatePolicy matrix.

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

src/Modules/TeamUp.Modules.Governance/Gate/HeldActionExecutor.cs

@@ -0,0 +1,30 @@
+using TeamUp.SharedKernel.Board;
+
+namespace TeamUp.Modules.Governance.Gate;
+
+/// <summary>
+/// Performs the internal action behind an agent proposal: write the artifact onto the task and
+/// create the proposed child tasks. Used by the gate (autonomous path) and the approve endpoint.
+/// </summary>
+internal sealed class HeldActionExecutor(IBoardWriter boardWriter)
+{
+    public async Task ExecuteAsync(
+        Guid teamId,
+        Guid workItemId,
+        string content,
+        IReadOnlyList<string> childTitles,
+        Guid? actedByMemberId,
+        CancellationToken cancellationToken = default)
+    {
+        if (!string.IsNullOrWhiteSpace(content))
+        {
+            await boardWriter.AttachArtifactAsync(workItemId, content, cancellationToken);
+        }
+
+        if (childTitles.Count > 0)
+        {
+            var children = childTitles.Select(title => new ChildTaskSpec(title, "Story")).ToList();
+            await boardWriter.CreateChildTasksAsync(teamId, workItemId, children, actedByMemberId, cancellationToken);
+        }
+    }
+}