Design: Flight boarding pass layout

[melvincarvalho]

Design PR — edits app.js + app.css only (no app files touched).

• Flight gets a boarding pass layout (class .card.boarding-pass)
  • Dark header strip: airline name + flight number in monospace
  • Route section: big airport codes (PRG → CDG) with city names and times beneath
  • Plane icon + dotted flight path between airports
  • Dashed tear line with semicircular notches
  • Fake barcode strip via CSS repeating-linear-gradient
  • Description as small footnote text
  • Dark mode support (strip inverts to white-on-dark)

Gate: 324 apps pass. Task: #IssDesign2_Flight.