chore(deps): remove dead Elasticsearch search-index builder and unused deps

[DeepDiver1975]

What

Removes the dead Elasticsearch search-index builder (ext-antora/generate-index.js) and the npm dependencies that only it consumed.

Why

The indexer only executed when UPDATE_SEARCH_INDEX=true and the ELASTICSEARCH_* env vars were set. The docs site aggregator no longer sets these and no longer ships this extension — search moved to pagefind — so the code path is dead. Carrying it kept a large transitive dependency tree (the elastic client, cheerio → parse5/entities, html-entities) that is a needless Dependabot attack surface.

Changes

• Drop @elastic/elasticsearch, cheerio, html-entities from dependencies (sole consumer was the indexer)
• Delete ext-antora/generate-index.js and its reference in site.yml
• Delete the orphan es-docker-compose.yml (Elasticsearch dev-stack file, referenced nowhere)
• Regenerate package-lock.json (343 → 315 locked packages)

js-yaml and asciidoctor-kroki are kept — still in use.

Verification

• npm install succeeds; lockfile no longer references elastic/cheerio/html-entities
• npm run antora still produces public/ output (the removed extension was a no-op outside the indexing env). The remaining xref not found warnings are pre-existing — site.yml sets failure_level: none because the standalone build lacks the sibling docs-* content sources.

🤖 Generated with Claude Code

[DeepDiver1975]

🤖 Automated review by Claude Code review agent.

Verdict: looks good — dead-code removal is clean and fully verified.

This drops the dead Elasticsearch search-index builder (ext-antora/generate-index.js), its three sole-consumer deps (@elastic/elasticsearch, cheerio, html-entities), the orphan es-docker-compose.yml, and regenerates the lockfile.

Verified: NO remaining references to the removed code or deps anywhere in the repo.
I cloned the PR head and grepped all *.js/*.json/*.yml/*.star/Makefile/*.sh/*.hbs/*.adoc (excluding package-lock.json) for elasticsearch|generate-index|cheerio|html-entities|es-docker-compose|UPDATE_SEARCH_INDEX|ELASTICSEARCH_ → zero matches.

• site.yml cleanly removes the ./ext-antora/generate-index.js extension line; its remaining extensions (load-global-site-attributes.js, find-orphaned-files.js, commented-out ones) all still exist on disk.
• package.json scripts (antora, antora-local, linkcheck, etc.) reference none of the removed pieces.
• CI (.github/workflows/ci.yml) only runs npm install + npm run antora; no ES/index step. No .drone.star in this repo.

package.json + lockfile consistency: ✅ The three deps are removed from dependencies, and the lockfile correctly prunes the whole transitive tree (cheerio-select, css-select/css-what, dom-serializer, domhandler, domutils, parse5*, htmlparser2, undici, boolbase, encoding-sniffer, whatwg-*, hpagent, secure-json-parse, nth-check). debug, ms, iconv-lite, safer-buffer are correctly retained but re-flagged dev: true (now only pulled in by dev deps) — consistent.

Obsolescence corroborated: The builder only ran under UPDATE_SEARCH_INDEX=true + ELASTICSEARCH_* env vars, set nowhere in this repo or its CI. The PR description notes search moved to pagefind; nothing here depends on the old ES path, so the code is genuinely dead.

Checks: Build documentation ✅ pass, lint ✅ pass.

Nicely scoped, reduces Dependabot surface, no functional risk. No changes requested.