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/mir/mod.rs

@@ -20,6 +20,8 @@ pub mod value_id;
 pub mod effect;
 pub mod optimizer;
 pub mod slot_registry; // Phase 9.79b.1: method slot resolution (IDs)
+#[cfg(feature = "aot-plan-import")]
+pub mod aot_plan_import;
 pub mod passes; // Optimization subpasses (e.g., type_hints)
 
 // Re-export main types for easy access