feat(automation): support public reply variations (#31)

[Cid-oe]

Summary

Resolves #31.

Allows rules to define multiple public reply variations (one per line or JSON array format), picking one at random per send using crypto.getRandomValues.

Changes

• Added parsePublicReplyVariations and selectPublicReply to src/process.ts.
• Integrated selectPublicReply into comment processing when sending public replies.
• Retained full backward compatibility for existing single-value text and blank values with zero migration needed.
• Empty/blank lines in variations are cleanly ignored.
• Updated admin rule form helper note on the public_reply_text textarea to explain line-separated variations.
• Added comprehensive unit tests in scripts/test-unit.ts covering single-value strings, multiline variations, blank lines, JSON array inputs, and random selection.

Validation

• npm test passed (48 tests pass).
• npm run typecheck passed cleanly.