docs(tui): fix stale cucumber runner count in harness header

The residue-cleanup commit corrected tests/README.md to five Gherkin
runners after the plugin_e2e_acceptance scenario deletion but left the
harness header saying "six feature runners / six link jobs"; drop the
count so the comment cannot drift again.

Signed-off-by: asto18089 <asto18089@126.com>

Author: asto18089

crates/tui/tests/cucumber/main.rs

@@ -1,9 +1,9 @@
 //! Consolidated harness for Gherkin/Cucumber runners.
 //!
 //! Cucumber (`cucumber = "0.23"`) registers steps per `World` type via
-//! inventory. Each `World` is scoped to its own `mod`, so merging the six
+//! inventory. Each `World` is scoped to its own `mod`, so merging the
 //! feature runners into one binary keeps `cargo test -p codewhale-tui
-//! tool_lifecycle` etc. filtering via the module path while cutting six link
+//! tool_lifecycle` etc. filtering via the module path while cutting link
 //! jobs to one. See `crates/tui/tests/README.md`.
 
 #[cfg(all(unix, feature = "long-running-tests"))]