Replace retrieval synonyms with glossary terms

## Parent

#406

## What to build

Replace unsupported alternate spellings of the package's core retrieval terms after the `parallel_chunks` explanation has been settled. Where "sub-request" denotes one piece of a split query, use chunk; where concurrency is described, use chunks in flight. Where "parallelism" denotes concurrent chunk execution, use fan-out.

Apply the correction across package prose, user documentation, examples, notebooks, comments, and wording-sensitive test messages. Preserve ordinary uses that are not synonyms, references in accepted decisions explaining rejected names, and the independent-item meaning of batch.

## Acceptance criteria

- [ ] "Sub-request" no longer denotes a chunk anywhere in tracked package, documentation, examples, notebooks, or tests.
- [ ] Concurrency descriptions consistently use chunks in flight.
- [ ] Uses of "parallelism" that denote concurrent chunk execution are rewritten as fan-out.
- [ ] Accepted-decision references to rejected names and ordinary behavioral uses remain unchanged.
- [ ] Batch terminology for independent-item skip policy remains unchanged.
- [ ] No public identifier, parameter, environment variable, signature, or runtime behavior changes.
- [ ] Repository-wide searches demonstrate that every remaining occurrence is an explicit exclusion rather than unresolved drift.
- [ ] Notebooks and documentation build successfully, and the offline suite, lint, type checker, and architecture checks pass.

## Blocked by

- #412

Start by reading parent issue #406 and the blocking issue #412 to understand the settled glossary terms. Search tracked package prose, documentation, examples, notebooks, comments, and wording-sensitive tests for the listed synonyms, preserving the explicit exclusions. Done means repository-wide searches show only intentional exclusions, documentation and notebooks build, and the offline suite, lint, type checker, and architecture checks pass.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.