Add unified cross-product search to the landing page

[willeastcott]

What

Adds a global search to the landing page that spans all products, so visitors no longer need to know which product a symbol lives in before they can search for it.

• build.mjs: new mergeSearchIndexes() step (runs in both full and --landing-only builds) decodes each product''s TypeDoc search index (window.searchData = base64, deflate-compressed JSON containing a serialized lunr 2.3.9 index), prefixes row URLs with the product folder, tags each row with a product-<folder> class, rebuilds a single combined index with TypeDoc-identical builder settings, and writes it to docs/assets/search.js. copySharedAssets() now also copies TypeDoc''s main.js and icons.js from the engine build.
• index.html: adds TypeDoc 0.28''s stock search trigger/dialog markup and script tags. The hand-rolled inline theme/menu handlers are removed since main.js now drives those elements (same markup contract the landing page already mirrors).
• assets/landing.css: styles the product-<folder> class as a badge (Engine, PCUI, ...) on each search result, themed via TypeDoc CSS variables.
• repos-config.json: new optional per-repo search fields — engine gets searchBoost: 1.25 and searchKindBoosts: {128: 2} (restores its TypeDoc searchGroupBoosts class boost, which is baked into the original index and lost on re-merge); engine-v1 is excluded via searchExclude to keep ~4,700 near-duplicate legacy symbols out (its own per-product search is untouched).
• package.json: adds lunr@2.3.9, pinned to match the version bundled in TypeDoc''s client.

Why reuse TypeDoc''s client instead of writing a custom search UI

The landing page already mirrors TypeDoc''s markup and reuses its stylesheet. Pointing TypeDoc''s own main.js at a combined index in the exact same format gets the dialog UX, ranking, Ctrl+K / / shortcuts, keyboard navigation, a11y, and graceful failure with zero client-side JS to maintain.

Notes for reviewers

• The combined index is 9,575 rows from 7 products, ~347 KB base64 — comparable to the engine''s own 206 KB per-product index, and loaded async the same way.
• The merge validates each product''s index (wrapper format + lunr version) and skips it with a build warning instead of failing, so TypeDoc format drift in one upstream repo degrades that product''s coverage rather than breaking the site. The coupling (searchData wrapper, deflate, lunr 2.3.9) is documented in the README.
• Verified locally against the full built docs/ tree: round-trip decode/query in Node, plus browser checks (search/keyboard shortcuts/theme toggle/mobile menu, light+dark themes, result navigation to /engine/classes/AppBase.html, missing-index failure modes).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a unified, cross-product search experience to the landing page by reusing TypeDoc’s built-in client UI and generating a merged search index during the build.

Changes:

• Introduces a build-time mergeSearchIndexes() step to decode each product’s TypeDoc search.js, rewrite URLs/classes, and emit a single combined docs/assets/search.js.
• Updates the landing page to use TypeDoc’s stock search trigger/dialog and loads TypeDoc client assets (main.js, icons.js, merged search.js).
• Adds per-repo search tuning (searchExclude, searchBoost, searchKindBoosts) and styles per-product result badges.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
build.mjs	Adds merged search index generation and copies TypeDoc client assets (main.js, icons.js) into shared landing assets.
index.html	Integrates TypeDoc search UI markup and scripts; removes the custom inline handlers now covered by main.js.
assets/landing.css	Styles product-<folder> classes as per-product badges in search results.
repos-config.json	Adds per-repo search config knobs and excludes engine-v1 from the combined index.
README.md	Documents how global search works, what’s merged, and the TypeDoc/lunr coupling.
package.json	Pins lunr devDependency to 2.3.9 to match TypeDoc’s client.
package-lock.json	Locks lunr@2.3.9 installation details.

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