fix(bridge): implement env.box_introspect.kind lowering + Stage0 build fixes

Phase 25.1b type system groundwork - env.* namespace support in Bridge layer

Changes:
- Bridge layer (JSON v0 → MIR):
  - Add 'env' as well-known variable in MapVars::resolve()
  - Implement env.box_introspect.kind(value) → ExternCall lowering
  - Pattern: Method { recv: Method { recv: Var("env"), method: "box_introspect" }, method: "kind" }

- VM/extern fixes:
  - Add Arc::from() conversion for env.box_introspect.kind result
  - Fix MapBox API usage in extern_functions.rs logging

- Build fixes:
  - Comment out missing llvm_legacy/llvm modules in src/backend/mod.rs
  - Comment out missing gui_visual_node_prototype in Cargo.toml

- New files:
  - lang/src/shared/common/box_type_inspector_box.hako (type introspection API)

Context:
- Enables BoxTypeInspectorBox to query runtime Box types via env.box_introspect.kind
- Required for selfhost MirBuilder type-aware lowering (multi-carrier loops, etc.)
- Part of Phase 25.1b "no fallback" selfhosting strategy

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

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

Cargo.toml

@@ -124,10 +124,10 @@ name = "gui_test_icon_extraction"
 path = "examples/test_icon_extraction.rs"
 required-features = ["gui-examples"]
 
-[[example]]
-name = "gui_visual_node_prototype"
-path = "development/egui_research/experiments/visual_node_prototype.rs"
-required-features = ["gui-examples"]
+# [[example]]
+# name = "gui_visual_node_prototype"
+# path = "development/egui_research/experiments/visual_node_prototype.rs"
+# required-features = ["gui-examples"]