docs: add agent skill bundle for coding assistants (SKILL.md, pipelines, convert/evaluate) (#3174)

* docs: add agent skill bundle with convert/evaluate helpers

- Add docs/examples/agent_skill/docling-document-intelligence/ with
  SKILL.md, pipelines.md, EXAMPLE.md, improvement-log template, and
  scripts/docling-convert.py + docling-evaluate.py (standard/vlm-local/vlm-api).
- Document InputFormat.PDF + PdfFormatOption for explicit PdfPipelineOptions.
- Link from examples index and mkdocs nav.

Made-with: Cursor

* docs: align agent skill README and EXAMPLE with Cursor bundle

- Document both ~/.cursor/skills and docs/examples paths.
- README notes repo parity for PRs and local installs.

Made-with: Cursor

* DCO Remediation Commit for jehlum11 <jehlum11@gmail.com>

I, jehlum11 <jehlum11@gmail.com>, hereby add my Signed-off-by to this commit: 2d268ffb6fcc4c0e09f9a1482204a2e2501123d4
I, jehlum11 <jehlum11@gmail.com>, hereby add my Signed-off-by to this commit: 041e709c66f23e15823b3249688b6222a0aa31d8

Signed-off-by: jehlum11 <jehlum11@gmail.com>
Made-with: Cursor

* docs: refactor agent skill to use docling CLI for conversion

Address maintainer feedback: the custom docling-convert.py script was
largely redundant with the existing docling CLI. This commit:

- Removes scripts/docling-convert.py (redundant with `docling` CLI)
- Refactors SKILL.md (v1.4 → v2.0) to use `docling` CLI for all
  conversion tasks, reserving the Python API only for features the
  CLI does not expose (chunking, VLM API endpoint config,
  force_backend_text hybrid mode)
- Updates docling-evaluate.py recommended_actions to reference
  `docling` CLI flags instead of the removed script
- Updates README.md, EXAMPLE.md, pipelines.md to use `docling` CLI
  examples throughout
- Simplifies requirements.txt (removes packaging dependency)

The only custom script retained is docling-evaluate.py, which provides
heuristic quality evaluation — functionality the CLI does not cover.

Signed-off-by: jehlum11 <jehlum11@gmail.com>
Made-with: Cursor

* docs: fix ruff format on docling-evaluate.py

Signed-off-by: jehlum11 <jehlum11@gmail.com>
Made-with: Cursor

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Signed-off-by: jehlum11 <jehlum11@gmail.com>