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>

tools/using_resolve_smoke.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+ROOT_DIR=$(CDPATH= cd -- "$SCRIPT_DIR/.." && pwd)
+BIN="$ROOT_DIR/target/release/nyash"
+
+if [ ! -x "$BIN" ]; then
+  cargo build --release --features cranelift-jit >/dev/null
+fi
+
+JSON=$(mktemp)
+cat >"$JSON" <<'JSON'
+{"version":0,"kind":"Program","body":[
+  {"type":"Return","expr":{"type":"Extern","iface":"env.modules","method":"get","args":[{"type":"Str","value":"Util"}]}}
+]}
+JSON
+
+# Use direct path using via CLI
+NYASH_DISABLE_PLUGINS=1 "$BIN" --backend vm --json-file "$JSON" \
+  --using '"apps/selfhost-minimal/main.nyash" as Util' > /tmp/nyash-using-resolve.out
+
+if rg -q '\.nyash' /tmp/nyash-using-resolve.out; then
+  echo "PASS: using resolve (CLI direct path)" >&2
+else
+  echo "FAIL: using resolve (CLI direct path)" >&2
+  sed -n '1,120p' /tmp/nyash-using-resolve.out >&2
+  exit 1
+fi
+
+echo "All PASS" >&2
+