feat(mir): Phase 63-6-1/2 MIR Phi type_hint field & JoinIR propagation

Phase 63-6-1: MirInstruction::Phi に type_hint フィールド追加
- Added `type_hint: Option<MirType>` field to Phi instruction
- Updated 21 files with type_hint initialization (all set to None for legacy paths)
- Pattern matching updated across codebase (11 files)
- Test code updated (basic_block.rs)

Phase 63-6-2: JoinIR→MIR Bridge で型ヒント伝播実装
- Modified convert.rs: Select → MIR now creates PHI with type_hint
- Removed Copy instructions from then/else blocks
- PHI instruction at merge block receives type_hint from JoinIR Select
- Test verification: ✅ Type hint propagation successful (Some(Integer))

Modified files:
- instruction.rs: Added type_hint field definition
- join_ir_vm_bridge/convert.rs: Select lowering with PHI + type_hint
- 19 other files: type_hint field initialization

Test results:
- ✅ test_type_hint_propagation_simple: Type hint = Some(Integer) confirmed
- ✅ 7/8 if_select tests passing (1 race condition, passes individually)

Next: Phase 63-6-3 (lifecycle.rs で型ヒント使用)

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

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

src/runner/json_v0_bridge/lowering/loop_.rs

@@ -163,6 +163,7 @@ impl LoopFormOps for LoopFormJsonOps<'_> {
                 if let MirInstruction::Phi {
                     dst,
                     inputs: phi_inputs,
+                    .. // Phase 63-6: Ignore type_hint
                 } = inst
                 {
                     if *dst == phi_id {

src/runner/json_v1_bridge.rs

@@ -273,6 +273,7 @@ pub fn try_parse_v1_to_module(json: &str) -> Result<Option<MirModule>, String> {
                         block_ref.add_instruction(MirInstruction::Phi {
                             dst: ValueId::new(dst),
                             inputs: pairs,
+                type_hint: None, // Phase 63-6
                         });
                         max_value_id = max_value_id.max(dst + 1);
                     }

src/runner/mir_json_emit.rs

@@ -227,7 +227,7 @@ pub fn emit_mir_json_for_harness(
                         }
                         continue;
                     }
-                    if let I::Phi { dst, inputs } = inst {
+                    if let I::Phi { dst, inputs, .. } = inst {
                         let incoming: Vec<_> = inputs
                             .iter()
                             .map(|(b, v)| json!([v.as_u32(), b.as_u32()]))
@@ -642,7 +642,7 @@ pub fn emit_mir_json_for_harness_bin(
                 let mut emitted_defs: std::collections::HashSet<u32> =
                     std::collections::HashSet::new();
                 for inst in &bb.instructions {
-                    if let I::Phi { dst, inputs } = inst {
+                    if let I::Phi { dst, inputs, .. } = inst {
                         let incoming: Vec<_> = inputs
                             .iter()
                             .map(|(b, v)| json!([v.as_u32(), b.as_u32()]))

src/runner/mir_json_v0.rs

@@ -179,6 +179,7 @@ pub fn parse_mir_v0_to_module(json: &str) -> Result<MirModule, String> {
                         block_ref.add_instruction(MirInstruction::Phi {
                             dst: ValueId::new(dst),
                             inputs: pairs,
+                type_hint: None, // Phase 63-6
                         });
                         max_value_id = max_value_id.max(dst + 1);
                     }