docs: add pipelines documentation and CLI usage

[samcday]

Motivation

• Provide user-facing documentation for the new pipeline descriptor model so readers can understand, author, and operate pipelines (leafs/wrappers/selectors, YAML shape, and common patterns).
• Surface CLI workflows and examples to make gibblox-cli pipeline actions (validate, encode, decode, and direct execution) discoverable and easy to follow.

Description

• Add docs/pipelines.md containing a conceptual overview, YAML examples (HTTP, local file + GPT, casync with/without chunk_store), and gibblox-cli usage examples.
• Update README.md with a new Pipelines section that links to the detailed guide in docs/pipelines.md.
• This is documentation-only and does not change runtime behavior or public APIs.

Testing

• Ran cargo check -p gibblox-cli, which completed successfully.
• No additional automated tests were added because the changes are documentation-only.

---

Codex Task

[samcday]

@codex rebase and update this PR

[chatgpt-codex-connector]

Summary

• Followed up on the docs PR with a new commit that clarifies pipeline validation behavior for YAML vs binary descriptors in the top-level README pipelines section. README.mdL61-L67
• Updated the detailed pipelines guide to explicitly include both pipeline validate (YAML) and pipeline validate --binary examples in the CLI workflow section. docs/pipelines.mdL66-L92
• Clarified the notes section so validate default behavior and --binary behavior are both stated directly. docs/pipelines.mdL108-L113
• Created a follow-up PR entry via make_pr after committing (ef60413), per your instruction.

Testing

• ✅ cargo check -p gibblox-cli
• ❌ git rebase 0939c9b457daeef4d6a14ca7a268ffe93ea82515 (failed: base SHA from PR metadata is not present in this local clone, so a true rebase onto that exact commit could not be executed here)
• ⚠️ curl -L -s 'https://duckduckgo.com/html/?q=git%20rebase%20pull%20request%20branch%20onto%20latest%20base' | head -n 5 (search endpoint returned no visible content in this environment)
• ⚠️ curl -L -s 'https://www.bing.com/search?q=git+rebase+pull+request+branch+onto+latest+base' | head -n 5 (search endpoint returned no visible content in this environment)

View task →