feat(joinir): Phase 135 P0 - ConditionLoweringBox allocator SSOT (ValueId collision fix)

## Summary
Root cause: ConditionLoweringBox was bypassing ConditionContext.alloc_value (SSOT allocator),
causing ValueId collisions between JoinIR condition params and lowered instructions.

## Changes
1. **ConditionLoweringBox (expr_lowerer.rs)**: Must use ConditionContext.alloc_value
   - Pass &mut ConditionContext to lower_condition (SSOT allocator)
   - Eliminates internal counter usage

2. **Allocator unification (condition_lowerer.rs, method_call_lowerer.rs)**:
   - Accept &mut dyn FnMut() -> ValueId as allocator parameter
   - Ensures all lowering paths use same SSOT allocator

3. **Boundary Copy deduplication (joinir_inline_boundary_injector.rs)**:
   - Deduplicate condition_bindings by dst
   - Fail-Fast if different sources target same dst (MIR SSA violation)

4. **Trim pattern fixes (trim_loop_lowering.rs, trim_pattern_validator.rs, stmts.rs)**:
   - Use builder.next_value_id() instead of value_gen.next() in function context
   - Ensures function-level ValueId allocation respects reserved PHI dsts

## Acceptance
✅ ./target/release/hakorune --verify apps/tests/phase133_json_skip_whitespace_min.hako
✅ Smoke: phase135_trim_mir_verify.sh - MIR SSA validation PASS
✅ Regression: phase132_exit_phi_parity.sh - 3/3 PASS
✅ Regression: phase133_json_skip_whitespace_llvm_exe.sh - compile-only PASS

🤖 Generated with Claude Code

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

src/mir/builder/stmts.rs

@@ -346,7 +346,8 @@ impl super::MirBuilder {
             }
             last_value = Some(var_id);
         }
-        Ok(last_value.unwrap_or_else(|| self.value_gen.next()))
+        // Phase 135 P0: Use function-level ValueId (SSOT) - build_local_statement is always in function context
+        Ok(last_value.unwrap_or_else(|| self.next_value_id()))
     }
 
     // Return statement