Upgrade live timing page for race weekends

- Track status flag banner (green/yellow/SC/VSC/red, defensive mapping)
- Weather strip: air/track temp, humidity, wind with compass, rain badge
- Gap trend sparklines from a per-driver interval ring buffer
- Battle detection: consecutive cars within 1.0s chained and highlighted
- Stint history column with compound sequence per driver
- Pinnable drivers (max 3) with focus cards, persisted to localStorage

Pure logic lives in lib/gapHistory.ts and lib/battles.ts with unit
tests; 137 frontend tests passing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/battles.ts

@@ -0,0 +1,107 @@
+// Battle detection for the live timing tower.
+// Pure functions only — no React, no side effects — so everything is unit-testable.
+
+import type { LiveTimingRow } from './live'
+import { driverCode } from './live'
+import { parseIntervalSeconds } from './gapHistory'
+
+export const BATTLE_THRESHOLD_SECONDS = 1.0
+
+export interface BattleDriver {
+  racingNumber: string
+  code: string
+  position: number
+  /** Interval to the car ahead within the group; null for the group leader. */
+  gapToAhead: number | null
+}
+
+export interface Battle {
+  drivers: BattleDriver[]
+  /** Tightest car-to-car interval within the group. */
+  minGap: number
+}
+
+/** Battles are only meaningful in race-type sessions (GP race, sprint). */
+export function isRaceSession(sessionType: string | null | undefined): boolean {
+  if (!sessionType) return false
+  const type = sessionType.toLowerCase()
+  return type.includes('race') || type.includes('sprint')
+}
+
+function isEligible(row: LiveTimingRow): boolean {
+  const driver = row.Driver
+  return Boolean(driver) && !driver.InPit && !driver.Retired && row.Position > 0
+}
+
+/**
+ * Scan position-sorted tower rows and group consecutive cars racing within
+ * `threshold` seconds of the car ahead. Cars in the pits or retired break
+ * the chain, as do lapped/unparsable intervals.
+ */
+export function detectBattles(
+  rows: ReadonlyArray<LiveTimingRow>,
+  sessionType: string | null | undefined,
+  threshold = BATTLE_THRESHOLD_SECONDS,
+): Battle[] {
+  if (!isRaceSession(sessionType) || rows.length < 2) return []
+
+  const battles: Battle[] = []
+  let current: BattleDriver[] | null = null
+  let minGap = Number.POSITIVE_INFINITY
+
+  const flush = () => {
+    if (current && current.length >= 2) {
+      battles.push({ drivers: current, minGap })
+    }
+    current = null
+    minGap = Number.POSITIVE_INFINITY
+  }
+
+  for (let i = 1; i < rows.length; i++) {
+    const ahead = rows[i - 1]
+    const row = rows[i]
+    const gap = parseIntervalSeconds(row.Driver?.Interval)
+
+    const inBattle =
+      gap !== null && gap >= 0 && gap <= threshold && isEligible(ahead) && isEligible(row)
+
+    if (!inBattle) {
+      flush()
+      continue
+    }
+
+    if (!current) {
+      current = [toBattleDriver(ahead, null)]
+    }
+    current.push(toBattleDriver(row, gap))
+    if (gap < minGap) minGap = gap
+  }
+  flush()
+
+  return battles
+}
+
+function toBattleDriver(row: LiveTimingRow, gapToAhead: number | null): BattleDriver {
+  return {
+    racingNumber: row.RacingNumber,
+    code: driverCode(row),
+    position: row.Position,
+    gapToAhead,
+  }
+}
+
+/** Chip label, e.g. "VER ⚔ NOR +0.4" or "VER ⚔ NOR ⚔ PIA +0.3". */
+export function battleLabel(battle: Battle): string {
+  const codes = battle.drivers.map((driver) => driver.code).join(' ⚔ ')
+  const gap = Number.isFinite(battle.minGap) ? ` +${battle.minGap.toFixed(1)}` : ''
+  return `${codes}${gap}`
+}
+
+/** Racing numbers involved in any battle, for tower row highlighting. */
+export function battleNumbers(battles: ReadonlyArray<Battle>): Set<string> {
+  const numbers = new Set<string>()
+  for (const battle of battles) {
+    for (const driver of battle.drivers) numbers.add(driver.racingNumber)
+  }
+  return numbers
+}