feat(vcs): add CommitID to ReviewRequest (#115)

Add CommitID string field to vcs.ReviewRequest so both platform
adapters can thread the commit anchor through the abstraction layer.

Changes:
- vcs/types.go: Add CommitID field with json tag commit_id,omitempty
- gitea/client.go: Re-add commitID parameter to PostReview (was
  removed during PR #112 refactoring)
- gitea/adapter.go: Forward req.CommitID to underlying client
- github/review.go: Use req.CommitID as primary anchor, fall back to
  comment-derived CommitID when empty, reject on conflict
- cmd/review-bot/main.go: Set ReviewRequest.CommitID = evaluatedSHA

Fixes #115

cmd/review-bot/main.go

@@ -485,7 +485,7 @@ func main() {
 	reviewReq := vcs.ReviewRequest{
 		Body:     reviewBody,
 		Event:    event,
-		CommitID: pr.Head.SHA,
+		CommitID: evaluatedSHA,
 		Comments: inlineComments,
 	}
 	posted, err := client.PostReview(ctx, owner, repoName, prNumber, reviewReq)

gitea/adapter_test.go

@@ -214,6 +214,40 @@ func TestAdapter_PostReview_EventTranslation(t *testing.T) {
 	}
 }
 
+
+func TestAdapter_PostReview_CommitID(t *testing.T) {
+	var gotCommitID string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		var payload struct {
+			CommitID string `json:"commit_id"`
+		}
+		json.NewDecoder(r.Body).Decode(&payload)
+		gotCommitID = payload.CommitID
+		json.NewEncoder(w).Encode(map[string]any{
+			"id":        1,
+			"body":      "test",
+			"user":      map[string]any{"login": "bot"},
+			"commit_id": payload.CommitID,
+		})
+	}))
+	defer server.Close()
+
+	client := gitea.NewClient(server.URL, "token")
+	adapter := gitea.NewAdapter(client)
+
+	_, err := adapter.PostReview(context.Background(), "owner", "repo", 1, vcs.ReviewRequest{
+		Body:     "test",
+		Event:    vcs.ReviewEventApprove,
+		CommitID: "sha256abc",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if gotCommitID != "sha256abc" {
+		t.Errorf("expected commit_id %q forwarded to client, got %q", "sha256abc", gotCommitID)
+	}
+}
 func TestAdapter_PostReview_WithComments_PositionTranslation(t *testing.T) {
 	diff := `diff --git a/main.go b/main.go
 --- a/main.go

gitea/client_test.go

@@ -147,6 +147,46 @@ func TestPostReview(t *testing.T) {
 	}
 }
 
+func TestPostReview_CommitID(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "POST" {
+			t.Fatalf("expected POST, got %s", r.Method)
+		}
+
+		body, _ := io.ReadAll(r.Body)
+		var payload struct {
+			Body     string `json:"body"`
+			Event    string `json:"event"`
+			CommitID string `json:"commit_id"`
+		}
+		if err := json.Unmarshal(body, &payload); err != nil {
+			t.Fatalf("unmarshal payload: %v", err)
+		}
+		if payload.CommitID != "deadbeef123" {
+			t.Errorf("expected commit_id %q, got %q", "deadbeef123", payload.CommitID)
+		}
+		if payload.Event != "APPROVED" {
+			t.Errorf("expected event APPROVED, got %q", payload.Event)
+		}
+
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(`{"id":101,"user":{"login":"review-bot"},"state":"APPROVED","stale":false,"commit_id":"deadbeef123"}`))
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL, "test-token")
+	review, err := client.PostReview(context.Background(), "owner", "repo", 3, "APPROVED", "LGTM", "deadbeef123", nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if review.ID != 101 {
+		t.Errorf("expected review ID 101, got %d", review.ID)
+	}
+	if review.CommitID != "deadbeef123" {
+		t.Errorf("expected commit_id %q, got %q", "deadbeef123", review.CommitID)
+	}
+}
+
 func TestGetPullRequest_Non200(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusNotFound)

vcs/types.go

@@ -98,6 +98,5 @@ type ReviewRequest struct {
 	// If empty, the platform defaults to the current PR head.
 	// Adapters use this as the primary commit anchor for the review submission.
 	CommitID string `json:"commit_id,omitempty"`
-
 	Comments []ReviewComment `json:"comments,omitempty"`
 }