fix: handle submit-package-job when Deadline CLI is installed via submitter installer

[crowecawcaw]

Fixes: #123

What was the problem/requirement? (What/Why)

The conda_recipes/submit-package-job wrapper script assumed the deadline command was always a pip-installed Python entry point script. On macOS/Linux it recovered the interpreter to use by reading the script's #! shebang line via head -1 "$DEADLINE_PATH" | cut -c 3-.

When the Deadline Cloud CLI is installed via the standalone submitter installer, deadline is instead a self-contained compiled binary (PyInstaller build) with no reusable Python interpreter. Feeding that binary to head -1 | cut hits a non-UTF-8 byte and fails with a cryptic error, leaving the user with no path forward:

$ sh submit-package-job aftereffects-25.1
cut: stdin: Illegal byte sequence

The only workaround was to uninstall the CLI and reinstall it via pip.

What was the solution? (How)

• submit-package-job — Added a DEADLINE_PYTHON environment variable override so users can point the wrapper at any Python that has the deadline library installed. Guarded the shebang read by verifying the file actually begins with #!, and emit an actionable error (instead of a cryptic cut failure) for both the installer-binary case and the case where deadline is not found on PATH.
• submit-package-job.bat — Mirrored the DEADLINE_PYTHON override and replaced the terse :nopython message with one that explains the installer limitation and how to resolve it.
• conda_recipes/README.md — Documented the Python interpreter requirement, the difference between pip install and the standalone installer, and how to use DEADLINE_PYTHON.

What is the impact of this change?

• Users who installed the CLI via the submitter installer can now submit package build jobs by setting DEADLINE_PYTHON to a Python that has the deadline library, without uninstalling/reinstalling.
• Users who hit an unsupported configuration get a clear, actionable error instead of cut: stdin: Illegal byte sequence.
• The existing pip install deadline auto-discovery path is unchanged and fully backward compatible.

How was this change tested?

Tested on macOS with two deadline installs present: a standalone submitter-installer binary (/Users/.../DeadlineClient/deadline, a Mach-O executable) and a pip-installed one (a shebang script).

Case 1 — installer binary first on PATH (previously failed with Illegal byte sequence):

$ ./submit-package-job aftereffects-25.1
ERROR: The 'deadline' command at '/Users/.../DeadlineClient/deadline' is not a pip-installed Python script (it looks like the standalone submitter installer build, which does not bundle a reusable Python interpreter).

submit-package-job needs a Python interpreter that has the 'deadline' library
installed. Set the DEADLINE_PYTHON environment variable to such an interpreter, e.g.:

    DEADLINE_PYTHON=python3 ./submit-package-job aftereffects-25.1

and ensure it has the library available (pip install deadline).

Case 2 — DEADLINE_PYTHON override (installer still first on PATH):

$ DEADLINE_PYTHON=python3 ./submit-package-job --help
usage: submit-package-job [-h] [-q QUEUE] [--s3-channel S3_CHANNEL] ...

Case 3 — pip-installed deadline first on PATH (auto-discovery, unchanged behavior):

$ ./submit-package-job --help
usage: submit-package-job [-h] [-q QUEUE] [--s3-channel S3_CHANNEL] ...

Case 4 — no deadline on PATH and no override:

$ ./submit-package-job blender-4.2
ERROR: Could not find the 'deadline' command on your PATH.
...

bash -n submit-package-job passes the syntax check.

Was this change documented?

Yes. Added a "Python interpreter requirement" section to conda_recipes/README.md covering the pip vs. standalone-installer cases and the DEADLINE_PYTHON override, plus a pointer to it from the prerequisites. Both wrapper scripts also gained explanatory header comments.

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