refactor(mir): Phase 137-6-S2 - dev-only で canonicalizer decision を提案として受け取る

## 目的
Canonicalizer の decision を router に差し込む（既定挙動不変）

## 変更内容

### choose_pattern_kind() に parity check 統合
- dev-only 時に Canonicalizer を呼び出し
- router_choice と canonical_choice を比較
- 不一致時の動作:
  - strict mode (`HAKO_JOINIR_STRICT=1`): panic (Fail-Fast)
  - debug mode (`NYASH_JOINIR_DEV=1`): ログのみ
- 既定挙動: router_choice を維持（Canonicalizer は提案のみ）

### ログ出力
```
[choose_pattern_kind/PARITY] OK: canonical and actual agree on Pattern2Break
```

## 効果
- ✅ Canonicalizer → Router の parity check 統合
- ✅ SSOT 入口での一致性検証
- ✅ 既定挙動完全不変（フラグOFF時）
- ✅ 新 env 追加なし（既存の `joinir_dev_enabled()` と `strict_enabled()` を使用）

## テスト結果
- ✅ `cargo build --release`: 成功
- ✅ skip_whitespace: parity green
  ```
  NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1 ./target/release/hakorune \
    tools/selfhost/test_pattern3_skip_whitespace.hako
  → [choose_pattern_kind/PARITY] OK
  ```
- ✅ スモークテスト（simple_*）: 5/5 PASS
- ✅ 退行なし

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/grammar/generated.rs

@@ -36,37 +36,15 @@ pub static OPERATORS_DIV_RULES: &[(&str, &str, &str, &str)] = &[
 ];
 pub fn lookup_keyword(word: &str) -> Option<&'static str> {
     for (k, t) in KEYWORDS {
-        if *k == word { return Some(*t); }
+        if *k == word {
+            return Some(*t);
+        }
     }
     None
 }
 
 pub static SYNTAX_ALLOWED_STATEMENTS: &[&str] = &[
-    "box",
-    "global",
-    "function",
-    "static",
-    "if",
-    "loop",
-    "break",
-    "return",
-    "print",
-    "nowait",
-    "include",
-    "local",
-    "outbox",
-    "try",
-    "throw",
-    "using",
-    "from",
+    "box", "global", "function", "static", "if", "loop", "break", "return", "print", "nowait",
+    "include", "local", "outbox", "try", "throw", "using", "from",
 ];
-pub static SYNTAX_ALLOWED_BINOPS: &[&str] = &[
-    "add",
-    "sub",
-    "mul",
-    "div",
-    "and",
-    "or",
-    "eq",
-    "ne",
-];
+pub static SYNTAX_ALLOWED_BINOPS: &[&str] = &["add", "sub", "mul", "div", "and", "or", "eq", "ne"];