feat: Support CircleCI CLI v1

[zahorniak]

Summary

Closes #43.

• Add a shared module circleci_cli.py. It detects the installed CLI generation at run time (legacy 0.1.x or CLI v1) and builds generation-correct commands.
• All four hooks translate their arguments automatically:
  • validate path: positional on legacy, --config <path> on v1 (v1 silently ignores a positional path, so this prevents wrong-file validation)
  • --org-slug/--org-id ⇄ --org (translation works in both directions, so one .pre-commit-config.yaml works for a team with mixed CLI versions)
  • --verbose → --debug on v1
• Fix an existing bug: the pack hook forwarded --org-slug/--org-id, but circleci config pack rejects these flags on both CLI generations. The hook now warns and does not forward them.
• Set CIRCLECI_CLI_SKIP_UPDATE_CHECK=true for all CLI calls. This makes legacy hook runs faster.
• README: link the new CLI download page (https://cli.circleci.com/), keep a legacy-labeled link, and document CLI version support and the v1 API-token requirement.

Test plan

• Full pytest suite: 87 passed (35 new/updated tests: detection, builders, per-hook translation on both generations)
• Smoke test with the real legacy binary (0.1.34038): validate exit 0, pack exit 0
• Smoke test with the real CLI v1 binary (1.0.46087-pre): validate reaches the API token gate with translated flags (no "unknown flag" error), pack exit 0