refactor(llvm): Complete Resolver pattern implementation across all instructions

Major structural improvement driven by ChatGPT 5 Pro analysis:
- Replace all direct vmap access with Resolver API calls
- Add proper cursor/bb_map/preds/block_end_values to all instruction handlers
- Ensure dominance safety by localizing values through Resolver
- Fix parameter passing in invoke/fields/extern handlers

Key changes:
- boxcall: Use resolver.resolve_i64/ptr instead of direct vmap access
- strings: Remove unused recv_v parameter, use Resolver throughout
- invoke: Add missing context parameters for proper PHI handling
- fields: Add resolver and block context parameters
- flow/arith/maps: Consistent Resolver usage pattern

This addresses the "structural invariant" requirements:
1. All value fetching goes through Resolver (no direct vmap.get)
2. Localization happens at BB boundaries via Resolver
3. Better preparation for PHI-only-in-dispatch pattern

Next: Consider boxing excessive parameters (15+ args in some functions)

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

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

src/backend/llvm/compiler/codegen/instructions/externcall/mod.rs

@@ -43,7 +43,7 @@ pub(in super::super) fn lower_externcall<'ctx, 'b>(
         return env::lower_local_get(codegen, cursor, resolver, cur_bid, func, vmap, dst, args, bb_map, preds, block_end_values);
     }
     if iface_name == "env.box" && method_name == "new" {
-        return env::lower_box_new(codegen, cursor, resolver, cur_bid, vmap, dst, args, bb_map, preds, block_end_values);
+        return env::lower_box_new(codegen, cursor, resolver, cur_bid, func, vmap, dst, args, bb_map, preds, block_end_values);
     }
 
     Err(format!(