Merge selfhosting-dev into main (Core-13 pure CI/tests + LLVM bridge) (#126)

* WIP: sync before merging origin/main

* fix: unify using/module + build CLI; add missing helper in runner; build passes; core smokes green; jit any.len string now returns 3

* Apply local changes after merging main; keep docs/phase-15 removed per main; add phase-15.1 docs and tests

* Remove legacy docs/phase-15/README.md to align with main

* integration: add Core-13 pure CI, tests, and minimal LLVM execute bridge (no docs) (#125)

Co-authored-by: Tomoaki <tomoaki@example.com>

---------

Co-authored-by: Selfhosting Dev <selfhost@example.invalid>
Co-authored-by: Tomoaki <tomoaki@example.com>

src/lib.rs

@@ -38,6 +38,10 @@ pub mod transport;
 
 // 🚀 MIR (Mid-level Intermediate Representation) Infrastructure (NEW!)
 pub mod mir;
+#[cfg(feature = "aot-plan-import")]
+pub mod mir_aot_plan_import {
+    pub use crate::mir::aot_plan_import::*;
+}
 
 // 🚀 Backend Infrastructure (NEW!)
 pub mod backend;