feat(llvm): Major refactor - BuilderCursor全域化 & Resolver API導入

Added:
- Resolver API (resolve_i64) for unified value resolution with per-block cache
- llvmlite harness (Python) for rapid PHI/SSA verification
- Comprehensive LLVM documentation suite:
  - LLVM_LAYER_OVERVIEW.md: Overall architecture and invariants
  - RESOLVER_API.md: Value resolution strategy
  - LLVM_HARNESS.md: Python verification harness

Updated:
- BuilderCursor applied to ALL lowering paths (externcall/newbox/arrays/maps/call)
- localize_to_i64 for dominance safety in strings/compare/flow
- NYASH_LLVM_DUMP_ON_FAIL=1 for debug IR output

Key insight: LoopForm didn't cause problems, it just exposed existing design flaws:
- Scattered value resolution (now unified via Resolver)
- Inconsistent type conversion placement
- Ambiguous PHI wiring responsibilities

Next: Wire Resolver throughout, achieve sealed=ON green for dep_tree_min_string

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

@@ -12,6 +12,7 @@ use crate::backend::llvm::compiler::codegen::instructions::builder_cursor::Build
 pub(in super::super) fn lower_externcall<'ctx, 'b>(
     codegen: &CodegenContext<'ctx>,
     cursor: &mut BuilderCursor<'ctx, 'b>,
+    resolver: &mut super::Resolver<'ctx>,
     cur_bid: BasicBlockId,
     func: &MirFunction,
     vmap: &mut HashMap<ValueId, BVE<'ctx>>,
@@ -19,13 +20,16 @@ pub(in super::super) fn lower_externcall<'ctx, 'b>(
     iface_name: &str,
     method_name: &str,
     args: &[ValueId],
+    bb_map: &std::collections::HashMap<crate::mir::BasicBlockId, inkwell::basic_block::BasicBlock<'ctx>>,
+    preds: &std::collections::HashMap<crate::mir::BasicBlockId, Vec<crate::mir::BasicBlockId>>,
+    block_end_values: &std::collections::HashMap<crate::mir::BasicBlockId, std::collections::HashMap<ValueId, BVE<'ctx>>>,
 ) -> Result<(), String> {
     // console/debug
     if (iface_name == "env.console"
         && matches!(method_name, "log" | "warn" | "error"))
         || (iface_name == "env.debug" && method_name == "trace")
     {
-        return console::lower_log_or_trace(codegen, cursor, cur_bid, vmap, dst, iface_name, method_name, args);
+        return console::lower_log_or_trace(codegen, cursor, resolver, cur_bid, vmap, dst, iface_name, method_name, args, bb_map, preds, block_end_values);
     }
     if iface_name == "env.console" && method_name == "readLine" {
         return console::lower_readline(codegen, cursor, cur_bid, vmap, dst, args);
@@ -33,13 +37,13 @@ pub(in super::super) fn lower_externcall<'ctx, 'b>(
 
     // env.*
     if iface_name == "env.future" && method_name == "spawn_instance" {
-        return env::lower_future_spawn_instance(codegen, cursor, cur_bid, vmap, dst, args);
+        return env::lower_future_spawn_instance(codegen, cursor, resolver, cur_bid, vmap, dst, args, bb_map, preds, block_end_values);
     }
     if iface_name == "env.local" && method_name == "get" {
-        return env::lower_local_get(codegen, cursor, cur_bid, func, vmap, dst, args);
+        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, cur_bid, vmap, dst, args);
+        return env::lower_box_new(codegen, cursor, resolver, cur_bid, vmap, dst, args, bb_map, preds, block_end_values);
     }
 
     Err(format!(