feat(joinir): promote joinir_runner_standalone_trim to mainline test

Remove #[ignore] from trim test, following skip_ws promotion pattern:
- NYASH_JOINIR_EXPERIMENT=1 toggle controls execution
- Normal cargo test skips via early return (lightweight)
- Two JoinIR standalone tests now available as PHI-independent baselines

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/tests/joinir_runner_standalone.rs

@@ -148,8 +148,10 @@ fn joinir_runner_standalone_skip_ws() {
 /// - Input: "   abc  " → Output: "abc  " (only leading spaces removed)
 /// - Input: "" → Output: ""
 /// - Input: "abc" → Output: "abc"
+///
+/// ## Phase 29 昇格 (2025-11-25)
+/// skip_ws に続いて本線テストに昇格。NYASH_JOINIR_EXPERIMENT=1 トグルで制御。
 #[test]
-#[ignore]
 fn joinir_runner_standalone_trim() {
     if !require_experiment_toggle() {
         return;