Update documentation for CLI, PGP, and Sigils

[google-labs-jules]

Added comprehensive documentation for the Trix CLI, PGP cryptographic operations, and a complete list of available sigils. Updated mkdocs.yml and index.md to include the new documentation pages.

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PR created automatically by Jules for task 7800286789416233870 started by @Snider

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✅ All modified and coverable lines are covered by tests.

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