fix(search): use lucide-react icons in SearchBar instead of unicode glyphs

[laurastephaniee]

Problem

SearchBar drew its search icon with a unicode 🔍 emoji inside a <span>. Everywhere else, the app uses lucide-react icons (NavBar: Menu/X, Breadcrumb: ChevronRight, Toast: X). The emoji:

• looks different on each OS and font (colourful on Apple, flat on Android/Windows) and ignores the text-gray-400 colour;
• doesn't match the rest of the UI's stroke icons;
• was announced by some screen readers as "magnifying glass tilted left".

The clear button had the same problem with a unicode ✕.

Changes

Commit 1: search icon (src/components/SearchBar.tsx)

• Imports Search from lucide-react and replaces the emoji <span>.
• size={16}, with the same positioning classes as before (absolute left-3 top-1/2 -translate-y-1/2, pointer-events-none), so it sits in the same place inside the existing pl-9 input padding.
• aria-hidden="true": it's decorative, and the input's placeholder describes the field.

Commit 2: clear icon + tests

• The clear button's ✕ is replaced with lucide X (size={14}, same as Toast), and aria-label="Clear search" is kept. The now-unused text-xs class is removed from the button.
• src/__tests__/SearchBar.test.tsx:
  • new test: the markup contains the lucide Search SVG (lucide-search), marked aria-hidden, and no 🔍;
  • the existing clear-button test also checks that the button renders a lucide X SVG and no ✕ glyph.

No new dependency: lucide-react is already in package.json.

Verification

• npx vitest run src/__tests__/SearchBar.test.tsx: 9/9 pass.
• tsc --noEmit reports no errors in the touched files.
  Closes [bug] SearchBar uses unicode magnifying glass emoji instead of icon component #651
  Closes [bug] buildFlightKey does not sanitize flight number input #616
  Closes [ux] Toast notification does not show timestamp #617
  Closes [security] Logo component priority prop defaults to true for all instances #618

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