feat(joinir): Phase 202-B Pattern 3 uses JoinValueSpace

Replace sequential value_counter (0u32) with JoinValueSpace allocator
in Pattern 3 (If-PHI) lowering for unified ValueId management.

Changes:
- loop_with_if_phi_minimal.rs: Replace value_counter with join_value_space.alloc_local()
- pattern3_with_if_phi.rs: Create JoinValueSpace and pass to lowerer
- loop_patterns/with_if_phi.rs: Update legacy wrapper to use JoinValueSpace

Benefits:
- Consistent with Pattern 2 implementation (Phase 201)
- Prevents ValueId collision in Local region (1000+)
- Clean separation: Param region (100-999) vs Local region (1000+)

Test status:
- All unit tests pass (5/5)
- E2E tests pass: loop_if_phi.hako, loop_if_phi_continue.hako

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

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

src/mir/builder/control_flow/joinir/patterns/pattern3_with_if_phi.rs

@@ -101,8 +101,12 @@ impl MirBuilder {
         // Phase 195: Use unified trace
         trace::trace().varmap("pattern3_start", &self.variable_map);
 
+        // Phase 202-B: Create JoinValueSpace for unified ValueId allocation
+        use crate::mir::join_ir::lowering::join_value_space::JoinValueSpace;
+        let mut join_value_space = JoinValueSpace::new();
+
         // Call Pattern 3 lowerer with preprocessed scope
-        let join_module = match lower_loop_with_if_phi_pattern(ctx.loop_scope) {
+        let join_module = match lower_loop_with_if_phi_pattern(ctx.loop_scope, &mut join_value_space) {
             Some(module) => module,
             None => {
                 // Phase 195: Use unified trace