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>

Makefile

@@ -0,0 +1,35 @@
+# Nyash selfhosting-dev quick targets
+
+.PHONY: build build-release run-minimal smoke-core smoke-selfhost bootstrap roundtrip clean quick fmt lint
+
+build:
+	cargo build --features cranelift-jit
+
+build-release:
+	cargo build --release --features cranelift-jit
+
+run-minimal:
+	NYASH_DISABLE_PLUGINS=1 ./target/release/nyash --backend vm apps/selfhost-minimal/main.nyash
+
+smoke-core:
+	bash tools/jit_smoke.sh
+
+smoke-selfhost:
+	bash tools/selfhost_vm_smoke.sh
+
+bootstrap:
+	bash tools/bootstrap_selfhost_smoke.sh
+
+roundtrip:
+	bash tools/ny_roundtrip_smoke.sh
+
+clean:
+	cargo clean
+
+quick: build-release smoke-selfhost
+
+fmt:
+	cargo fmt --all
+
+lint:
+	cargo clippy --all-targets --all-features -- -D warnings || true