Fix UI polish and stale app state

[ccchaos12]

What changed

• Apply a restrained Apple-inspired visual system using platform typography, quieter materials, consistent spacing, and accessible interaction feedback.
• Fix uneven card padding, duplicate bottom borders, inappropriate monospace detail text, and disabled-button hover movement.
• Invalidate cached summaries, filter options, searches, and counts when the SQLite file at the configured path changes.
• Preserve prepared CSV downloads across unrelated Streamlit reruns while invalidating them when filters or the database revision changes.
• Add regression coverage for same-path SQLite updates and persistent prepared exports.

Why

The previous UI had several small alignment and typography defects. More importantly, Streamlit cache entries were keyed only by the database path, so replacing a SQLite database at the same path could leave stale summary and search state visible until cache expiry or restart. Prepared CSV state was also transient.

Data integrity

No SQLite database or database query module was changed. K values, Reference data, filtering semantics, deduplication behavior, and source provenance remain unchanged. Core record counts and SHA-256 checks were revalidated before publication.

Validation

• Ruff lint passed.
• Python compilation passed.
• 60 unit and Streamlit tests passed.
• Git diff and CSS parsing checks passed.
• Streamlit health endpoint passed.
• Responsive and accessibility rules were checked for desktop, tablet, mobile, reduced motion, reduced transparency, and high contrast.
• Database invariants verified: 90,105 source records; 90,090 distinct records; 18,392 references; 60,756 default log K records; 60,771 including strict duplicates.