Add documentation validation

[MylesJP]

This commit introduces documentation validation system that ensures our published CLI examples remain executable and up to date with the product available to users. Note this initial PR is set to dry run only. See the Follow Up section below for a description of future work.

Summary of Changes:

• ci/select-doc-pages.py: builds an ordered execution plan from changed snippet files and their declared dependencies (# @Depends:).
• ci/run-doc-pages.py: extracts and runs (or dry-runs) [docs-exec:*] blocks from snippet files in sequential order.
• [docs-view:*] blocks: used for display in documentation via literalinclude, ensuring examples in the docs match what CI validates.
• Unit tests for both selector and runner using pytest.
• Updated GitHub Actions workflow for automatic snippet validation.
• Added ci/README.md explaining the framework, usage, and conventions.

Follow-up:

• Turn off DOCS_DRY_RUN to enable CI execution of documentation snippets. This is recommended as a subsequent PR to limit the testing footprint of snippet files and ease troubleshooting any issues.

[freyes]

nit, you can achieve the same with something like this:

- name: Foo
  run: |
    #!/bin/bash
    for FOO in $(ls *.txt); do
    ...

note: I won't block the PR on this, it's more a personal preference that allows to keep the interpreter that will be used and the code together