feat(tools): add DA plugin to generate FAQPage JSON-LD

[sdmcraft]

Summary

Adds a DA library plugin (tools/plugins/json-ld-schema/) that reads a page's .faq block content and generates FAQPage JSON-LD for the author to copy to clipboard and paste into the page's json-ld metadata row.

Grew out of the manual FAQPage JSON-LD work done across #451/#484/#485 — this makes that workflow self-serve instead of requiring an engineer to hand-generate it per page. Full plan, decisions, and prior-art review logged in #486.

• Extracts Q&A from any .faq-classed block (variant classes like faq cmp included), de-duplicating exact repeats and flattening multi-paragraph/list answers with word-boundary-safe joins (avoids the "answers run together" bug hit in a previous code-level attempt, PR feat(seo): add dynamic JSON-LD (BreadcrumbList + FAQPage) #472).
• Merges the generated FAQPage node into any existing json-ld metadata @graph by @type — verified idempotent (re-running doesn't duplicate nodes).
• Resolves the @id in order: existing WebPage node in the page's own json-ld → a plain canonical/url metadata key → the current aem.page URL.
• Copy-to-clipboard only — no write-back to the document. A direct-PUT approach via the DA Source API was considered and dropped: it isn't a Y.js delta and can conflict with an open live-editing session. Reading the source is safe; writing it isn't, so insertion happens through the normal DA editor instead.

Reuses parseMetadata(), buildSourceUrl(), buildPageUrl(), and pick() from an external reference plugin (usman-khalid/da-playground/tools/json-ld-generator); FAQ extraction and @graph merge logic are new, ported from the Python script used to fix #451/#484.

Verification

• Ran the extraction/merge functions (Node + JSDOM) against the real, live content/index.html — correctly parsed its existing 5-node @graph, resolved @id to https://erp.intuit.com/, and produced the same 5-node output on a second pass (no duplication).
• Verified the no-existing-json-ld case produces the plain (non-@graph) object format used across all 40 pages from SEO : JSON-LD : Add FAQPage JSON-LD schema (homepage — content already exists, schema is missing) #451/SEO : JSON-LD : Add FAQPage JSON-LD schema to remaining 41 pages with .faq blocks (follow-up to #451) #484.
• eslint (airbnb-base) and stylelint both pass clean.
• Not yet tested live inside the DA editor — this plugin needs to be registered in the site's DA library config sheet before it can be opened from the Library panel, and that registration requires DA site-admin permissions this session doesn't have (see Tooling: DA plugin to generate FAQPage JSON-LD and copy to clipboard #486 discussion). Marking as draft until that's confirmed working end-to-end.

Test plan

• Register in DA library config sheet (title: JSON-LD Schema, path: /tools/plugins/json-ld-schema/json-ld-schema.html, experience: dialog) — needs a DA org admin
• Open a page with a .faq block in the DA editor, launch the plugin from the Library panel, confirm the preview UI renders
• Confirm "Copy to clipboard" works and pasted value is valid JSON
• Confirm re-running on a page that already has json-ld merges rather than duplicates

Closes #486

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Commits

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