Add clang-format config, pre-commit hooks, and CI lint workflow

[hguillen]

Summary

• Adds the .clang-format config (Google C++ style) and .pre-commit-config.yaml that CONTRIBUTING.md and README.md reference but were missing from the repo
• Adds pre-commit to the Docker build image
• Adds a CI lint workflow that runs pre-commit on changed files inside the Docker container

Changes

File	Purpose
.clang-format	Google C++ style, 100-column limit
.pre-commit-config.yaml	clang-format v15, trailing-whitespace, end-of-file-fixer, check-yaml
scripts/Dockerfile	Added pre-commit to the Python venv pip installs
.github/workflows/lint.yml	PR lint workflow: builds Docker image, runs pre-commit run --from-ref origin/main --to-ref HEAD inside container

Design decisions

• Changed files only, not --all-files. Avoids a bulk reformat of the existing codebase. A full-repo reformat can be a separate follow-up.
• Runs inside Docker to match the build environment. No tools installed on bare runners.
• Separate workflow from PR verification (which is in a separate PR). Can be merged into pr-verify.yml later.

Test plan

• Verify lint workflow triggers on this PR
• Verify pre-commit installs correctly in the Docker image
• Verify clang-format runs on changed .cpp/.cu/.h files
• Verify workflow passes when changed files are correctly formatted

[hguillen]

@coderabbitai full review