feat(ui): add active/inactive panel border colors for #71

[vaishnavi003-svg]

Description

Add active/inactive panel border colors to improve focus clarity.

• Active panel gets bright border (highlight_color)
• Inactive panels get dim gray border (border_color)

Fixes #71

Type of Change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Manual test (please describe)

Tested with:

• Press e → search input border becomes bright

• Press Tab → package list border becomes bright

• Press j/k in details pane → details panel border becomes bright

• Other panels remain dim gray

• cargo test

Checklist:

• My code follows the Coding Guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have NOT added useless AI-generated comments.
• I have NOT deleted existing unrelated comments.
• I have NOT modified files unrelated to this task.
• I have included screenshots/recordings (for UI changes).
• My changes generate no new warnings (clippy/fmt).
• I have linked the issue I am working on.

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[pie-314]

@vaishnavi003-svg go through contribution docs, you need to raise pr in dev branch.
Screen Record/screenshot is applicable.