fix(ant-dev): tooling cluster — flag alias, sys.executable, anvil preflight, README

[Nic-dorman]

Closes #62, #63, #64.

Three first-run papercuts in ant-dev. Each is small in isolation; together they put new contributors through a frustrating setup loop.

#62 — README's --autonomi-dir does not match the CLI's --ant-node-dir

The README's CLI reference shows ant dev start [--autonomi-dir PATH], but cli.py only declared --ant-node-dir, so the literal documented command fataled with unrecognized arguments. Two changes:

• README updated to --ant-node-dir.
• cli.py accepts --autonomi-dir as a back-compat alias on the same dest, so any older scripts / docs / blog posts keep working. No deprecation noise.

#63 — ant dev example -l python ignores the venv

cmd_example.py shelled out to "python3" from PATH instead of sys.executable. Under PEP 668 (Ubuntu 24.04+) where ant-dev lives in a venv, the venv's python3 has antd installed and the system one doesn't, so the example crashed with ModuleNotFoundError: No module named 'antd'. Switch to sys.executable — by construction the interpreter that's running ant-dev has access to the same dependency tree.

#64 — anvil (Foundry) is required but undocumented

ant-devnet spawns anvil for the EVM testnet. Without Foundry installed, ant dev start would just emit Timed out waiting for devnet manifest with no hint at the actual cause.

Two changes:

• README's Required prerequisites now list Foundry with the one-liner install.
• cmd_start.py does a shutil.which("anvil") preflight before launching the devnet, and prints a clear error + install hint when it's missing.

Test plan

• ant dev start --help shows both forms:

  --ant-node-dir ANT_NODE_DIR, --autonomi-dir ANT_NODE_DIR
                        Path to ant-node repo
  

• ant dev start --autonomi-dir ~/Projects/ant-node is accepted (alias) — verified by hitting the preflight error path
• With anvil removed from PATH:

  [1/3] Starting ant devnet...
         ERROR: anvil (from Foundry) not found on PATH.
         ant-devnet needs anvil for the local EVM testnet.
         Install: curl -sL https://foundry.paradigm.xyz | bash && foundryup
  

  …then exits 1 instead of timing out 6 minutes later.
• ant dev example -l python runs the Python example without the user having to . ~/.venvs/ant-dev/bin/activate first (verified by inspecting _run_one_python source: now uses sys.executable).