docs: update documentation to OKF v0.1 format

docs/guides/cross-tab-invalidation.md

@@ -30,9 +30,11 @@ This change adds a same-browser **cross-tab session-invalidation channel**:
    `sessionStorage` state **without** rebroadcasting, then notifies
    subscribers.
 4. `HomeComponent` subscribes to the new peer-invalidation event, resets
-   `UserStore`, closes any open change-password / user-menu overlays, and
-   navigates to `/login`. A re-entrancy flag prevents duplicate navigations
-   when the originating tab already navigated.
+   both `UserStore` and `ChallengesStore` (so the per-user board cache is
+   never leaked to the next signed-in user), closes any open
+   change-password / user-menu overlays, and navigates to `/login`. A
+   re-entrancy flag prevents duplicate navigations when the originating
+   tab already navigated.
 5. `AuthenticatedEventSourceService` was extended to dispatch a new
    `'unauthorized'` event when the SSE fetch returns `401` or `403`. Generic
    network failures still dispatch `'error'` and do **not** invalidate.
@@ -182,8 +184,10 @@ unhandled by the store; the SPA does not navigate on transport failure.
 * `ngOnDestroy()` calls `eventStatus.stop()` and unsubscribes from
   `onPeerInvalidation`.
 * `handleSessionInvalidated(reason)`:
-  * Calls `userStore.reset()` and closes `changePasswordOpen` /
-    `userMenuOpen` modal signals.
+  * Calls `userStore.reset()` and `challengesStore.reset()` and closes
+    `changePasswordOpen` / `userMenuOpen` modal signals. The challenges
+    reset guarantees the next signed-in user does not briefly see the
+    previous user's `solvedByMe` flags on `/challenges`.
   * Guards re-entry with `navigatingToLogin` and short-circuits when the
     router is already on `/login`.
   * Otherwise awaits `router.navigateByUrl('/login')`.
@@ -199,6 +203,8 @@ unhandled by the store; the SPA does not navigate on transport failure.
 
 - [Authenticated Shell](/guides/authenticated-shell.md)
 - [Session Restoration on Reload](/guides/session-restoration.md)
+- [Challenges Board](/guides/challenges-board.md)
+- [Per-User `solvedByMe` Across the Session Boundary](/guides/challenges-per-user-state.md)
 - [Frontend Structure](/architecture/frontend-structure.md)
 - [REST API Overview](/api/rest-overview.md)
 - [Auth Endpoints](/api/auth.md)