fix: correct vfx_pipeline build docs and frame/publish edge cases

[crowecawcaw]

What

Follow-up to #258. A post-merge review surfaced a few issues in the newly added job_bundles/vfx_pipeline sample; this PR fixes them. All changes are confined to that sample.

Fixes

• Documented build command failed as written. The rattler-build build command in the sample README (twice) and the conda_channel README runs the recipe's post-build test, which must solve blender — available only in the farm's deadline-cloud channel, not on a workstation. The build exited non-zero and left no package, so the next step published an empty channel. Added --test skip (with an explanation) to all three build commands, and fixed the local conda create test command to include the deadline-cloud channel that provides Blender.
• Placeholder Flow project id rendered before failing. project.yaml ships project_id: 0. Because "0" is non-empty it passed the preSubmission hook's required-variable check, so a shot with publishing enabled rendered every frame (real farm cost) and only then failed in PublishToFlow against project 0. The hook now rejects FlowProjectId == 0 at submit time with a clear message when publishing is enabled.
• Single-frame range crashed the scripts. render_shot.py, encode_movie.py, and make_thumbnail.py did start, end = frame_range.split("-"), which raised ValueError for a bare single frame like FrameRange=5 (a valid OpenJD range). They now handle the no-- case. (Step ranges and comma lists remain unsupported, as before.)
• studio-pipe submit pass-through help. Clarified that extra args for deadline bundle submit go after a -- separator (e.g. -- --yes), matching the README and how argparse routes them.

Verification

• openjd check passes on the template.
• scripts/validate_repository.py passes (unit tests + local link check).
• Simulated the preSubmission hook: publish + project 0 fails fast, publish + real project passes, publish-off + project 0 passes.
• Single-frame parse verified for 1-48, 5, and 1-1.

Opening as a draft.

• Bundle README local-render snippet failed verbatim. It enabled the add-on with --addon-module but never set BLENDER_USER_SCRIPTS, and used unrunnable paths (bare scripts/... from a CWD where studio/ is two levels up, plus a .../ placeholder). Replaced it with a pointer to the working top-level walkthrough, and noted the tested Blender version (4.2+). Found by running every documented step locally.