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/origin/phi.rs

@@ -11,7 +11,7 @@ pub(crate) fn propagate_phi_meta(
     let mut common_ty: Option<MirType> = None;
     let mut ty_agree = true;
     for (_bb, v) in inputs.iter() {
-        if let Some(t) = builder.value_types.get(v).cloned() {
+        if let Some(t) = builder.type_ctx.value_types.get(v).cloned() {
             match &common_ty {
                 None => common_ty = Some(t),
                 Some(ct) => {
@@ -28,14 +28,14 @@ pub(crate) fn propagate_phi_meta(
     }
     if ty_agree {
         if let Some(ct) = common_ty {
-            builder.value_types.insert(dst, ct);
+            builder.type_ctx.value_types.insert(dst, ct);
         }
     }
     // Origin一致のときだけコピー
     let mut common_cls: Option<String> = None;
     let mut cls_agree = true;
     for (_bb, v) in inputs.iter() {
-        if let Some(c) = builder.value_origin_newbox.get(v).cloned() {
+        if let Some(c) = builder.type_ctx.value_origin_newbox.get(v).cloned() {
             match &common_cls {
                 None => common_cls = Some(c),
                 Some(cc) => {
@@ -52,7 +52,7 @@ pub(crate) fn propagate_phi_meta(
     }
     if cls_agree {
         if let Some(cc) = common_cls {
-            builder.value_origin_newbox.insert(dst, cc);
+            builder.type_ctx.value_origin_newbox.insert(dst, cc);
         }
     }
 }