refactor(mir): Remove TypeContext legacy fields (Phase 2-3/7)

完全移行→削除の安全順序（Option C）に従い、TypeContext の
deprecated フィールドと sync helpers を完全削除。

⚠️ 危険ゾーン: TypeFactsBox 等の同名フィールドと混同しないよう、
ファイル単位で手作業移行を実施。

## Changes
- Migrated all MirBuilder access sites to type_ctx.* (manual, 40+ files)
- Removed 3 deprecated fields (value_types, value_kinds, value_origin_newbox)
- Removed 2 sync helpers (sync_type_ctx_to_legacy, sync_legacy_to_type_ctx)
- Verified TypeFactsBox, CalleeGuardBox unchanged (no false positives)

## Tests
- cargo test --release --lib: 1029/1033 PASS
- TypeFactsBox integration: PASS (borrowed references unchanged)
- Deprecation warnings: 456 → 255 (-201, -44%)

## Safety Verification
✅ TypeFactsBox unchanged (still uses &'a BTreeMap borrowed references)
✅ CalleeGuardBox unchanged
✅ CalleeResolverBox unchanged
✅ BoxCompilationContext unchanged

Phase 2 Progress: 3/7 contexts complete (43%)
- ✅ MetadataContext
- ✅ CoreContext
- ✅ TypeContext (this commit)

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

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

src/mir/builder/exprs.rs

@@ -306,9 +306,9 @@ impl super::MirBuilder {
                     args: vec![],
                     effects: super::EffectMask::MUT,
                 })?;
-                self.value_origin_newbox
+                self.type_ctx.value_origin_newbox
                     .insert(arr_id, "ArrayBox".to_string());
-                self.value_types
+                self.type_ctx.value_types
                     .insert(arr_id, super::MirType::Box("ArrayBox".to_string()));
                 // TypeRegistry + trace for deterministic debug
                 self.type_registry
@@ -350,9 +350,9 @@ impl super::MirBuilder {
                     args: vec![],
                     effects: super::EffectMask::MUT,
                 })?;
-                self.value_origin_newbox
+                self.type_ctx.value_origin_newbox
                     .insert(map_id, "MapBox".to_string());
-                self.value_types
+                self.type_ctx.value_types
                     .insert(map_id, super::MirType::Box("MapBox".to_string()));
                 self.type_registry
                     .record_newbox(map_id, "MapBox".to_string());
@@ -401,10 +401,10 @@ impl super::MirBuilder {
     }
 
     fn infer_index_target_class(&self, target_val: ValueId) -> Option<String> {
-        if let Some(cls) = self.value_origin_newbox.get(&target_val) {
+        if let Some(cls) = self.type_ctx.value_origin_newbox.get(&target_val) {
             return Some(cls.clone());
         }
-        self.value_types.get(&target_val).and_then(|ty| match ty {
+        self.type_ctx.value_types.get(&target_val).and_then(|ty| match ty {
             super::MirType::Box(name) => Some(name.clone()),
             super::MirType::String => Some("String".to_string()),
             super::MirType::Integer => Some("Integer".to_string()),