Add DRP CLI, extensible linter, packaging entry point, and validation workflow

[safal207]

Motivation

• Provide a simple, standard CLI to run the existing DRP validator over files and globs and to surface results in a human-friendly colored format.
• Provide a lightweight, extensible linter for style and best-practice guidance for DRP records so projects can opt-in to non-blocking hygiene checks.
• Make the CLI installable via a console_scripts entry point so CI and developers can call drp-validate consistently.
• Add a dedicated GitHub Actions workflow to run validation on examples/*.json for push and PRs to main.

Description

• Added drp_cli.py, a small CLI wrapper that supports validation of one or more paths/globs, a --strict placeholder flag, an optional --lint run-after-validation flag, and a lint subcommand; it prints ANSI-colored output and returns a non-zero exit code when validation fails. The CLI uses the existing validator API (tools/drp_validator).
• Added linter.py, an extensible linter with a Warning dataclass, a @register_rule decorator for rule registration, and the requested baseline rules: record_id format, timestamp recommendation for decisions, priority recommendation for root decisions, causal_trace linkage recommendation, and non-empty content.description checks; provides lint_record and lint_data helpers.
• Added setup.py packaging metadata with a console_scripts entry point so pip install . exposes drp-validate.
• Added .github/workflows/drp_validate.yml which installs the package on Python 3.10 and runs drp-validate examples/*.json (blocking) and drp-validate --lint examples/*.json (non-blocking).
• Added basic tests tests/test_drp_cli_linter.py covering path expansion and a simple lint rule behavior.

Testing

• Ran unit tests: python -m pytest tests/test_drp_cli_linter.py -q, which passed (2 passed).
• Ran CLI smoke validation: python drp_cli.py examples/minimal_valid.json succeeded and reported the example as valid.
• Ran CLI linting modes: python drp_cli.py --lint examples/minimal_valid.json and python drp_cli.py lint examples/minimal_valid.json which ran and reported lint warnings (non-blocking) as expected.
• The added GitHub Actions workflow (.github/workflows/drp_validate.yml) is present and configured to run drp-validate against examples/*.json on push and pull_request to main (workflow not executed as part of these local tests).

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Codex Task