fix(portals): reload Stalker categories only for a held destination

Review follow-ups (Greptile, Codex): resetCategories() reloaded the
category resource, and the route session calls it on a portal switch
before the destination is resolved and on teardown, so it asked the
portal being left, and a failed destination lookup could let that answer
repopulate the sidebar. resetCategories() now only clears; the session
calls the new reloadCategories() after installing the destination, and
only when a handoff had already put that playlist in the store (the
owner, and so the resource params, did not change).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/stalker-portal.md

@@ -397,8 +397,12 @@ Category arrays belong to `categoryPlaylistKey`, not just the content type.
 Every category reader checks that owner; a portal switch clears all four
 section caches before loading the destination. Aborted or foreign-portal
 responses (including errors and radio fallbacks) cannot write into the active
-cache. Explicit category resets reload even when the playlist object remains
-unchanged. This contract applies to collection details as well as routed
+cache. `resetCategories()` only clears: the route session calls it on a
+portal switch before the destination is resolved and on teardown, where a
+request would go to the portal being left. When a handoff had already put
+the destination in the store, the owner does not change and the resource
+would not reload by itself, so the session calls `reloadCategories()` once
+it has installed that playlist. This contract applies to collection details as well as routed
 catalogs, because both use the root Stalker store.
 
 Failure-handling rule:

docs/architecture/stalker-store-api-baseline.md

@@ -93,6 +93,9 @@ During refactor:
 - `clearSelectedItem(): void`
 - `setCategories(type: 'vod' | 'series' | 'itv' | 'radio', categories: StalkerCategoryItem[]): void`
 - `resetCategories(): void`
+  Clears only; it starts no request (called on portal switches and route teardown).
+- `reloadCategories(): void`
+  Refetches the current portal's categories after a reset that keeps the owner.
 - `setItvChannels(channels: StalkerItvChannel[]): void`
 - `setRadioChannels(channels: StalkerItvChannel[]): void`
 - `setSearchPhrase(phrase: string): void`