docs: add Pundit policy adapter examples

[kholdrex]

Summary

Adds Pundit-focused policy adapter guidance for Rails reporting endpoints. The guide shows how to keep CodeToQuery behind existing authorization, return structured fail-closed predicates, and avoid logging sensitive prompts or bind values.

Changes

• Adds a Pundit policy adapter examples guide covering tenant, account, and user predicates.
• Links the guide from the README policy adapter section.
• Records the documentation addition in the changelog.
• Packages docs files with the gem so README links resolve from packaged documentation.

Test plan

• Verified Markdown links resolve locally.
• Verified Ruby snippets in the new guide parse successfully.
• Verified the gem builds and includes the new docs page, README, and changelog.
• Ran whitespace checks on the staged diff.