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/components/live/TimingTower.tsx

@@ -12,6 +12,9 @@ import {
   tyreLabel,
 } from '../../lib/live'
 import type { GapHistoryMap } from '../../lib/gapHistory'
+import { parseIntervalSeconds } from '../../lib/gapHistory'
+import { intervalMeaning } from '../../lib/meaning'
+import { Meaning } from '../Meaning'
 import { GapSparkline } from './GapSparkline'
 import { StintHistory } from './StintHistory'
 import { Pin } from 'lucide-react'
@@ -100,7 +103,11 @@ export function TimingTower({
             const showCutoffAfter = row.Position === sessionDisplay.cutoffPosition
 
             const gapText = gapMode === 'interval' && isRace ? (driver.Interval || driver.GapToLeader) : driver.GapToLeader
-            
+            const intervalAnnotation =
+              gapMode === 'interval' && isRace && row.Position > 1
+                ? intervalMeaning(parseIntervalSeconds(gapText))
+                : null
+
             const renderSector = (idx: number) => {
               const sec = driver.Sectors?.[idx]
               if (!sec) return '-'
@@ -149,7 +156,14 @@ export function TimingTower({
                   <td className={driver.LastLapOB ? 'mono lap-ob' : driver.LastLapPB ? 'mono lap-pb' : 'mono'}>
                     {driver.LastLapTime || '-'}
                   </td>
-                  <td className="mono">{gapText || '-'}</td>
+                  <td className="mono">
+                    <Meaning
+                      value={gapText || '-'}
+                      meaning={intervalAnnotation?.caption}
+                      title={intervalAnnotation?.title}
+                      tone={intervalAnnotation?.tone}
+                    />
+                  </td>
                   
                   {isRace && (
                     <td className="spark-cell">