feat(joinir): Phase 188 JoinInlineBoundary + Pattern 1 working! 🎉

Major milestone: loop_min_while.hako outputs "0 1 2" correctly!

## JoinInlineBoundary (Option D from ChatGPT Pro design review)
- New struct for clean SSA boundary between JoinIR and host function
- JoinIR uses local ValueIds (0,1,2...) - no host ValueId dependency
- Copy injection at entry block connects host → JoinIR values

## Pattern 1 Simple While Loop
- Refactored to use pure local ValueIds
- Removed Pattern1Context dependency on host ValueIds
- Clean separation: lowerer generates, merger connects

## Key Design Principles (Box Theory)
- Box A: JoinIR Frontend (host-agnostic)
- Box B: Join→MIR Bridge (independent functions)
- Box C: JoinInlineBoundary (boundary info only)
- Box D: JoinMirInlineMerger (Copy injection)

## Files Changed
- NEW: inline_boundary.rs - JoinInlineBoundary struct
- control_flow.rs - merge with boundary, void return fix
- simple_while_minimal.rs - pure local ValueIds
- mod.rs - module export

Test: NYASH_DISABLE_PLUGINS=1 ./target/release/hakorune apps/tests/loop_min_while.hako
Output: 0\n1\n2 ✅

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

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

src/mir/join_ir/lowering/mod.rs

@@ -27,6 +27,7 @@ pub mod if_merge; // Phase 33-7
 pub mod if_phi_context; // Phase 61-1
 pub mod if_phi_spec; // Phase 61-2
 pub mod if_select; // Phase 33
+pub mod inline_boundary; // Phase 188-Impl-3: JoinIR→Host boundary
 pub mod loop_form_intake;
 pub mod loop_patterns; // Phase 188: Pattern-based loop lowering (3 patterns)
 pub mod loop_scope_shape;