[hygiene] Duplicated validator line, unpinned docs deps, no lint/issue templates

Summary

A few low-severity code/repo hygiene items found during a developer review. Grouping them into one issue since each is small.

Findings

1. Triple-duplicated line in a validator. nv_core/sr_specs/docs/capabilities/core/atomic_asset/validation.py defines the same line three times (lines 27, 31, 35):

ZipFile = getattr(Usd, "ZipFile", getattr(Sdf, "ZipFile", object))

Two copies are dead; looks like a copy-paste or merge artifact. Keep one.

2. Unpinned documentation dependencies. requirements-docs.txt pins nothing:

nvidia-sphinx-theme
sphinx-copybutton
sphinx-design
sphinxcontrib-mermaid
myst-parser

A breaking upstream release can change or break the published docs with no code change. Pin or set upper bounds, and consider a lockfile for the docs build.

3. No lint/format/type config. No ruff/black/mypy config and no .pre-commit-config.yaml at the repo root. For a spec repo with Python validators, a formatter + linter + a pre-commit hook would keep contributions consistent.

4. No issue/PR templates. No .github/ISSUE_TEMPLATE/ and no .github/PULL_REQUEST_TEMPLATE.md. CONTRIBUTING.md currently states PRs aren't being accepted, which makes a structured bug/spec-issue template (like the form these review issues had to be written free-hand into) the more valuable of the two to add.

Why it matters

None of these are urgent, but together they're the difference between a repo that's easy to contribute to and verify vs. one that drifts. The duplicated validator line and unpinned docs deps are the two worth fixing soon.

Verified on main @ 2026.04.1, 2026-05-28.

Start by reviewing nv_core/sr_specs/docs/capabilities/core/atomic_asset/validation.py and requirements-docs.txt, then inspect the repository root and .github paths for existing configuration. Separate the four hygiene findings into concrete, independently verifiable changes, and confirm the validator has one definition, documentation dependencies are constrained, contributor checks are configured, and the relevant templates exist.