Add Rust ownership fusion theory and fix smoke test paths

🦀📦 Added Rust×Nyash ownership fusion design (Phase 17+ candidate)
- Comprehensive ownership integration proposal with tags + borrowing tokens
- 3-tier safety levels (Safe/Unsafe/FFI) with opt-in adoption
- Complete link integration across roadmap and docs

🔧 Fixed smoke test path resolution
- Corrected ROOT_DIR calculation in selfhost smoke tests
- Updated scopebox_identity_smoke.sh, loopform_identity_smoke.sh, selfhost_runner_smoke.sh

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

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

tools/test/smoke/selfhost/loopform_identity_smoke.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-ROOT_DIR=$(cd "$(dirname "$0")/../../.." && pwd)
+ROOT_DIR=$(cd "$(dirname "$0")/../../../.." && pwd)
 cd "$ROOT_DIR"
 
 echo "[smoke] build nyash (release)"

tools/test/smoke/selfhost/scopebox_identity_smoke.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-ROOT_DIR=$(cd "$(dirname "$0")/../../.." && pwd)
+ROOT_DIR=$(cd "$(dirname "$0")/../../../.." && pwd)
 cd "$ROOT_DIR"
 
 echo "[smoke] build nyash (release)"

tools/test/smoke/selfhost/selfhost_runner_smoke.sh

@@ -3,7 +3,7 @@ set -euo pipefail
 
 # Smoke: Stage 0/1 selfhost runner wiring (harness JSON path)
 
-ROOT_DIR=$(cd "$(dirname "$0")/../../.." && pwd)
+ROOT_DIR=$(cd "$(dirname "$0")/../../../.." && pwd)
 cd "$ROOT_DIR"
 
 echo "[smoke] building nyash (release)"