feat(frontend): annotate key numbers with meaning (#18)

Add shared Meaning primitive and pure interpretation helpers for interval,
tyre age, and championship gap columns on the live tower, tyre deg panel,
and championship hub. Thresholds are exported consts (undercut window tied
to PIT_LOSS_SECONDS from #13).

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/test/TyreDegPanel.test.tsx

@@ -52,9 +52,18 @@ describe('TyreDegPanel', () => {
     const panel = screen.getByTestId('tyredeg-panel')
     expect(panel).toHaveTextContent('VER')
     expect(panel).toHaveTextContent('M +5')
+    expect(panel).toHaveTextContent('fresh')
     expect(panel).toHaveTextContent('warming up')
   })
 
+  it('annotates tyre age meaning on stint rows', () => {
+    const rows = [
+      makeRow('1', 1, 'VER', { NumberOfLaps: 10, LastLapTime: '1:30.000' }, { Compound: 'MEDIUM', Age: 12 }),
+    ]
+    render(<TyreDegPanel rows={rows} sessionType="Race" pinned={[]} />)
+    expect(screen.getByText('mid-life')).toBeInTheDocument()
+  })
+
   it('renders slope and rejoin estimate once laps accumulate across snapshots', () => {
     const { rerender } = render(
       <TyreDegPanel rows={snapshotRows(1, '1:30.000')} sessionType="Race" pinned={[]} />,