v1.0.2 — fix diagram creation on pip installs

Patch release — reverts a v1.0.1 shim-writer regression that broke diagram creation for every pip-installed user with:

```
ENOTDIR: not a directory, mkdir '/datalex/diagrams'
```

Install

```bash
pip install --upgrade datalex-cli
```

Fixed

• `datalex/diagrams/` mkdir no longer collides with a file shim. v1.0.1 wrote a file named `datalex` next to the project root, which blocked the `mkdir datalex/diagrams/` that fires when the user clicks "new diagram". v1.0.2 stops writing that shim — the api-server's `dmExec()` helper already handles the `datalex → dm → PATH` fallback without any file named `datalex`.
• Self-heal on upgrade. If a v1.0.1 `datalex serve` already wrote the stray file, `datalex serve` now removes it on next start (only when it's our shebang signature — never a real user folder).

Upgrade guidance

If you installed v1.0.1 and hit the ENOTDIR error, upgrade and re-run `datalex serve` — the self-heal will clean up the stale shim automatically.

See CHANGELOG.md for full details.