fix: address review feedback on PR #106

- Remove unused envOrDefaultBool function and its test (Sonnet #3266 NIT)
- Replace Unicode em dashes with ASCII in slog messages (GPT #3267 NIT)
- Add scheme validation for vcsURL before embedding in Markdown link
  (Security #3269 MINOR — defense-in-depth against unsafe schemes)
- Extract ReviewerSelfRequester interface to remove concrete gitea.Adapter
  dependency from main's self-reviewer path (Sonnet #3266 NIT)
- Add compile-time conformance assertion and test for Adapter.RequestReviewerSelf

gitea/adapter_test.go

@@ -386,3 +386,25 @@ func TestAdapter_GetFileContent_RefRouting(t *testing.T) {
 		t.Errorf("GetFileContent(ref=\"abc123\") = %q, want %q", got, "content-at-ref")
 	}
 }
+
+func TestAdapter_RequestReviewerSelf(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		expected := "/api/v1/repos/owner/repo/pulls/5/requested_reviewers"
+		if r.URL.Path != expected {
+			t.Errorf("path = %q, want %q", r.URL.Path, expected)
+		}
+		w.WriteHeader(http.StatusCreated)
+	}))
+	defer server.Close()
+
+	client := gitea.NewClient(server.URL, "token")
+	adapter := gitea.NewAdapter(client)
+
+	err := adapter.RequestReviewerSelf(context.Background(), "owner", "repo", 5, "bot-user")
+	if err != nil {
+		t.Fatalf("RequestReviewerSelf() error = %v", err)
+	}
+}