fix(#75): preserve Race Hub meeting/session on Weekend return

Add an explicit Back to Weekend link that deep-links to /?meeting_key&session_key,
restore that focus on the adaptive Weekend home with a Continue analysis CTA, and
regenerate Race Hub visual baselines against the integrated #80 nav.

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

frontend/src/lib/routeSearch.ts

@@ -0,0 +1,40 @@
+/** Shared URL search contracts for deep-linkable Weekend ↔ Race Hub navigation. */
+
+export type WeekendSearch = {
+  meeting_key?: number
+  session_key?: number
+}
+
+export type RaceHubSearch = {
+  session_key?: number
+}
+
+function parsePositiveInt(value: unknown): number | undefined {
+  const n = Number(value)
+  return Number.isFinite(n) && n > 0 ? n : undefined
+}
+
+export function parseWeekendSearch(search: Record<string, unknown>): WeekendSearch {
+  const meeting_key = parsePositiveInt(search.meeting_key)
+  const session_key = parsePositiveInt(search.session_key)
+  return {
+    ...(meeting_key ? { meeting_key } : {}),
+    ...(session_key ? { session_key } : {}),
+  }
+}
+
+export function parseRaceHubSearch(search: Record<string, unknown>): RaceHubSearch {
+  const session_key = parsePositiveInt(search.session_key)
+  return session_key ? { session_key } : {}
+}
+
+/** Build Weekend `/` search so a Race Hub return is reload-safe and deep-linkable. */
+export function weekendFocusSearch(
+  meetingKey?: number | null,
+  sessionKey?: number | null,
+): WeekendSearch {
+  return {
+    ...(meetingKey && meetingKey > 0 ? { meeting_key: meetingKey } : {}),
+    ...(sessionKey && sessionKey > 0 ? { session_key: sessionKey } : {}),
+  }
+}