ci: validate extracted fable stack

[saagpatel]

Purpose

Temporary integration-only PR to run the repository's native GitHub Actions matrix against the exact union of upstream draft PRs devwhodevs#45 through devwhodevs#49.

This branch contains no additional product changes. It combines, in dependency-safe order:

• deterministic equal-score search ordering (fix(search): make equal-score ranking deterministic devwhodevs/engraph#46)
• read-only serve maintenance safety (fix(serve): disable writer maintenance in read-only mode devwhodevs/engraph#49)
• embedding-context reuse with parity evidence (perf(llm): reuse embedding context across batch inputs devwhodevs/engraph#45)
• indexed-model status metadata (feat(status): report indexed embedding metadata devwhodevs/engraph#48)
• model-free integration test replacement (test: replace obsolete model integration suites devwhodevs/engraph#47)

Lifecycle

This PR exists only to capture macOS and Ubuntu integration evidence while upstream fork-workflow runs await maintainer approval. After checks finish, it will be closed and its remote branch deleted. The five upstream PRs remain the reviewable delivery units.

Refs devwhodevs#44.

[saagpatel]

Temporarily closing and reopening to trigger the newly registered inherited CI workflow; no code changes.

[saagpatel]

Cross-platform validation passed on macOS and Ubuntu. Closing this temporary integration-only PR and deleting its aggregate branch; upstream PRs devwhodevs#45-devwhodevs#49 remain the review units.