Stabilize the Details dashboard layout

[domcyrus]

Summary

• replace dynamic Details sections with stable Connection, Network Context, Application, and Transport Health cards
• keep missing DNS, GeoIP, DPI, and transport values in fixed placeholder rows
• align RX and TX traffic cards with the dashboard columns and stabilize current-rate and peak positions
• preserve the original field list on narrow terminals
• add snapshot and alignment regression coverage

Why

Optional connection metadata previously added and removed rows, which shifted the lower sections while navigating. Traffic statistics also used an independent three-column layout, so its labels did not share the dashboard grid.

The new layout keeps important visual anchors fixed across connection types and metadata availability.

Validation

• cargo test --all-targets
• cargo clippy --all-targets -- -D warnings
• live macOS preview with GeoIP enabled
• live macOS preview with --no-geoip