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/fields.rs

@@ -16,7 +16,7 @@ impl super::MirBuilder {
 
         // Unified members: if object class is known and has a synthetic getter for `field`,
         // rewrite to method call `__get_<field>()`.
-        if let Some(class_name) = self.value_origin_newbox.get(&object_value).cloned() {
+        if let Some(class_name) = self.type_ctx.value_origin_newbox.get(&object_value).cloned() {
             if let Some(map) = self.property_getters_by_box.get(&class_name) {
                 if let Some(kind) = map.get(&field) {
                     let mname = match kind {
@@ -57,8 +57,8 @@ impl super::MirBuilder {
             .get(&(object_value, field.clone()))
             .cloned()
         {
-            self.value_origin_newbox.insert(field_val, class_name);
-        } else if let Some(base_cls) = self.value_origin_newbox.get(&object_value).cloned() {
+            self.type_ctx.value_origin_newbox.insert(field_val, class_name);
+        } else if let Some(base_cls) = self.type_ctx.value_origin_newbox.get(&object_value).cloned() {
             // Cross-function heuristic: use class-level field origin mapping
             if let Some(fcls) = self
                 .field_origin_by_box
@@ -73,13 +73,13 @@ impl super::MirBuilder {
                         base_cls, field, fcls
                     ));
                 }
-                self.value_origin_newbox.insert(field_val, fcls);
+                self.type_ctx.value_origin_newbox.insert(field_val, fcls);
             }
         }
 
         // If base is a known newbox and field is weak, emit WeakLoad (+ optional barrier)
         let mut inferred_class: Option<String> =
-            self.value_origin_newbox.get(&object_value).cloned();
+            self.type_ctx.value_origin_newbox.get(&object_value).cloned();
         if inferred_class.is_none() {
             if let ASTNode::FieldAccess {
                 object: inner_obj,
@@ -128,7 +128,7 @@ impl super::MirBuilder {
         value_result = self.local_arg(value_result);
 
         // If base is known and field is weak, create WeakRef before store
-        if let Some(class_name) = self.value_origin_newbox.get(&object_value).cloned() {
+        if let Some(class_name) = self.type_ctx.value_origin_newbox.get(&object_value).cloned() {
             if let Some(weak_set) = self.weak_fields_by_box.get(&class_name) {
                 if weak_set.contains(&field) {
                     value_result = self.emit_weak_new(value_result)?;
@@ -158,7 +158,7 @@ impl super::MirBuilder {
         })?;
 
         // Write barrier if weak field
-        if let Some(class_name) = self.value_origin_newbox.get(&object_value).cloned() {
+        if let Some(class_name) = self.type_ctx.value_origin_newbox.get(&object_value).cloned() {
             if let Some(weak_set) = self.weak_fields_by_box.get(&class_name) {
                 if weak_set.contains(&field) {
                     let _ = self.emit_barrier_write(value_result);
@@ -167,11 +167,11 @@ impl super::MirBuilder {
         }
 
         // Record origin class for this field value if known
-        if let Some(val_cls) = self.value_origin_newbox.get(&value_result).cloned() {
+        if let Some(val_cls) = self.type_ctx.value_origin_newbox.get(&value_result).cloned() {
             self.field_origin_class
                 .insert((object_value, field.clone()), val_cls.clone());
             // Also record class-level mapping if base object class is known
-            if let Some(base_cls) = self.value_origin_newbox.get(&object_value).cloned() {
+            if let Some(base_cls) = self.type_ctx.value_origin_newbox.get(&object_value).cloned() {
                 self.field_origin_by_box
                     .insert((base_cls, field.clone()), val_cls);
             }