extra facets from the url for channel page

[abeglova]

What are the relevant tickets?

closes https://github.com/mitodl/hq/issues/12383

Description (What does it do?)

#3655 updates the main search to add extra facets if there is a filter in the url. This does the same for channel searches. Filter parameters that are part of the saved filter for the channel are ignored

How can this be tested?

http://open.odl.local:8062/c/unit/ocw?level=undergraduate should show the level facet

http://open.odl.local:8062/c/unit/ocw?offered_by=ocw and http://open.odl.local:8062/c/unit/ocw?offered_by=mitxonline should look exactly like the normal ocw unit search

[github-actions]

OpenAPI Changes

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[Copilot]

Pull request overview

Extends the “show facets implied by URL filters” behavior (introduced for the main search page) to channel searches, so channel pages can surface and request aggregations for facets that appear in the URL even when they’re not part of that channel type’s default facet set. This fits into the shared SearchDisplay + request-building flow by ensuring both SSR prefetch and client-side channel search compute consistent facet manifests/aggregation lists.

Changes:

• Pass URL search params into channel facet computation so URL-implied facets are included in facetNames/facetManifest.
• Add channel-specific logic to compute “extra facet names” from the URL while excluding channel defaults and channel-config (saved) filters.
• Add ChannelPage tests verifying extra facets are aggregated/rendered and that default facets are not duplicated.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
frontends/main/src/app/(site)/c/[channelType]/[name]/page.tsx	Builds URLSearchParams from Next.js search params and passes them into channel facet calculation for SSR prefetch.
frontends/main/src/app-pages/ChannelPage/searchRequests.ts	Computes extra facet names from URL params (excluding defaults/saved filters) and threads them into the channel facet manifest + facet name list.
frontends/main/src/app-pages/ChannelPage/ChannelSearch.tsx	Passes current URL search params into getFacets so client-side rendering matches SSR behavior.
frontends/main/src/app-pages/ChannelPage/ChannelSearch.test.tsx	Adds coverage for URL-surfaced facets and ensures no duplication for facets already shown by default.