NO-TICKET: docs: Add instrumentation README template and generated module docs

[SenNeonoveNoci]

Adds a shared instrumentation README template, guidelines, and Codex skill for generating consistent module documentation. Generates README files for all integration/<module> instrumentations and links the process from CONTRIBUTING.md and agents.md so future instrumentation changes include matching documentation updates.

Checklist

• My code follows the project's coding standards.
• I have run linters/formatters and fixed any issues.
• There are no merge conflicts.
• I have performed a self-review of my code.
• All new and existing tests pass locally.
• I have added license headers to all files.

Generative AI usage

• GAI was not used (or, no additional notation is required)
• Coder created a draft manually that was non-substantively modified by GAI (e.g., refactoring was performed by GAI on manually written code)
• GAI was used to create a draft that was subsequently customized or modified
• Code was generated entirely by GAI