v1.7.0: private repository-aware reviews without timeline noise

What's new in v1.7.0

• Later pushes now update Cody's existing review comment instead of posting a new one each time. Set update_existing_comment: "false" to keep the old behavior.
• New inputs: review_instructions (repository-specific review priorities), exclude_paths (glob patterns excluded from review), context_files (guidance files for the reviewer), and max_diff_chars (validated cap on the diff size sent to the model).
• Review guidance files (AGENTS.md, REVIEW.md, CLAUDE.md, .github/copilot-instructions.md) are read from the pull request's trusted base commit, so a pull request cannot alter its own review rules.
• Path exclusion uses real glob semantics: ** crosses directories (including zero), * and ? stay within one path segment.
• A pull request whose changed files are all excluded is treated as a valid review instead of an Action failure.
• The documented install workflow uses pull_request_target with no checkout of pull-request code, enforced by regression tests in the repository.
• Added SECURITY.md, CONTRIBUTING.md, and issue/PR templates.