feat: read changelog from public/changelog.json, drop Webflow/Algolia dep

[markshenouda]

Summary

• Switches the changelog UI to read directly from public/changelog.json at build time, removing the runtime Algolia Changelog index lookup from changelog.astro, changelog/[...id].astro, and ChangelogSnippet.astro.
• Adds src/utils/changelog.ts, which ports slug / description / related-tokens / related-networks HTML generation from chainlink-webflow-cms-api/chainlog-handler.js, plus a category→label map (integration, release, deprecation, feature, update, cre, dta, ace, with title-cased fallback for anything else). Uses marked (already a dep) instead of pulling in showdown.
• Bonus fix in a separate commit: the changelog page's search input previously took priority and silently ignored active filter chips. Now a row must match both the search term and the filters when both are active.

Closes #290.

Why

The changelog data is already authored in public/changelog.json (mirrored from smartcontractkit/documentation). Round-tripping it through Webflow → Algolia → the docs site was the reason new categories like deprecation, cre, dta, ace were silently dropped: chainlog-handler.js skipped any entry whose category didn't match a slug in the Webflow Chainlog types collection. Reading the JSON directly removes that bottleneck and makes the data the single source of truth.

Follow-up

Once this is verified in prod, a separate cleanup PR in chainlink-webflow-cms-api can delete chainlog-handler.js, the npm run chainlog workflow step, the Changelogs-v2s Algolia generator entry, and the chainlog schema validator. The @algolia/client-search package is also no longer used in src/ and can be dropped from package.json (left for the follow-up since this PR is already across multiple files).

Test plan

• `/changelog` renders with the existing styling; Deprecated, Feature, Update, CRE entries all show the correct type chip
• Type filter lists "Deprecated" (and the other new categories) and filters correctly
• Product/network/type filter combinations work as before
• Search + active filter now combine (was the bonus fix)
• Individual entry page (`/changelog/`) renders with the entry's actual type in the H1 (was hardcoded to "Integration")
• CCIP page `ChangelogSnippet` shows the latest CCIP entry
• Mobile breakpoint