Feat: enhance package pinning

[mexirica]

Fix #126.

Greptile Summary

This PR enhances package pinning and repository filtering behavior. The main changes are:

• Adds a separate ᴾ indicator for packages matched by APT preferences rules.
• Loads package-specific preferences from /etc/apt/preferences and preferences.d during package refresh.
• Keeps APTUI favorite pins distinct from system policy pins in the UI and docs.
• Improves quoted and escaped repo: filter parsing.
• Preserves repository origins across multiple available package versions.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

_{Reviews (3): Last reviewed commit: "Feat: implement package-specific APT pre..." | Re-trigger Greptile}