feat(config): add complete and minimal gittensory config templates

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Summary

Add repo-level configuration templates that show both a minimal recommended setup and the full supported configuration surface with defaults, comments, and allowed values.

Context

Repo maintainers need a clearer way to understand what can be configured without reverse-engineering runtime behavior. The full template should be exhaustive and documented; the minimal template should be small enough for a new self-hoster to start safely.

Requirements

• Inventory every current repo-scoped and self-host review setting.
• Define stable config names, default values, allowed values, and validation behavior.
• Add a complete template, likely gittensory.yml, with comments for all supported options.
• Add a minimal template, likely gittensory.minimal.yml, with practical defaults.
• Keep compatibility with existing private repo-config behavior.
• Avoid exposing secrets or environment-specific values in templates.

Deliverables

• Complete config template with comments and allowed values.
• Minimal config template for getting started.
• Parser/validator updates if needed.
• Documentation showing precedence between file config, private config, and environment settings.
• Tests for defaults, invalid values, and backwards compatibility.

Acceptance criteria

• A maintainer can answer “what can I configure?” from the template alone.
• Existing repo configs continue to work unchanged.
• Invalid config values fail clearly before a review runs.