Use a portable relative default for the PeTTa checkout path

The PY_LIVE differential defaulted `PETTA_DIR` to a hardcoded home directory
(`/home/user/Dev/PeTTa`), which leaked into the published README and only
resolved on one machine. Default to `../PeTTa` instead: it resolves to the same
place when PeTTa sits beside the repo and the suite is run from the root, and
the differential still skips (not fails) when the checkout is absent.

Author: MesTTo

packages/py/README.md

@@ -117,7 +117,7 @@ startup and long Python calls can block rendering.
 
 The unit and property tests run with no Python, against an in-process fake bridge. Two suites reach a real interpreter and are gated:
 
-- `PY_LIVE=1 pnpm vitest run packages/py` runs the pythonia end-to-end tests and the byte-parity differential against a live PeTTa checkout (`PETTA_DIR`, default `/home/user/Dev/PeTTa`).
+- `PY_LIVE=1 pnpm vitest run packages/py` runs the pythonia end-to-end tests and the byte-parity differential against a live PeTTa checkout (`PETTA_DIR`, default `../PeTTa`).
 - `HYPERON_LIVE=1 pnpm vitest run packages/py` runs the differential against pip `hyperon`. Set one up with `uv venv --python 3.11 .venv-hyperon && uv pip install -p .venv-hyperon hyperon` (override the interpreter with `HYPERON_PY`).
 - `PYODIDE_LIVE=1 pnpm vitest run packages/py/src/pyodide.test.ts`
   starts real Pyodide and checks `.py` import plus `py-call`.

packages/py/src/py-differential.test.ts

@@ -5,7 +5,7 @@
 // Differential oracle: the same corpus through live PeTTa (SWI + janus) and through
 // @metta-ts/py + pythonia, comparing the (RESULT ...) line sequences byte-for-byte on the parity
 // surface, and asserting mutual failure on the error corpus. Gated on PY_LIVE=1; the PeTTa checkout
-// is PETTA_DIR (default /home/user/Dev/PeTTa). The helper defs (PY_METTA_SRC) are prepended to both
+// is PETTA_DIR (default ../PeTTa). The helper defs (PY_METTA_SRC) are prepended to both
 // sides, so the corpus needs no library import.
 import { describe, it, expect, beforeAll, afterAll } from "vitest";
 import { execFileSync } from "node:child_process";
@@ -17,7 +17,7 @@ import { setOutputSink, runProgramAsync, format } from "@metta-ts/core";
 import { PY_METTA_SRC, pyCoreAsyncOps, type PyBridge } from "./index";
 import { makePythoniaBridge } from "./live-bridge";
 
-const PETTA = process.env.PETTA_DIR ?? "/home/user/Dev/PeTTa";
+const PETTA = process.env.PETTA_DIR ?? "../PeTTa";
 const LIVE = process.env.PY_LIVE === "1" && existsSync(join(PETTA, "run.sh"));
 const d = LIVE ? describe : describe.skip;