Generate CLI docs from Go code

[bfirsh]

This implements CLI documentation generation using cobra/doc, building on the work started in #1696.

Changes

• Add tools/gendocs/ Go tool to generate CLI reference docs from cobra commands
• Generate docs/cli.md programmatically from Go source code
• Add mise tasks:
  • mise run docs:cli - generate CLI docs
  • mise run docs:cli:check - verify docs are up to date
• Run CLI docs check in CI alongside llms.txt check
• Update AGENTS.md with CLI docs maintenance instructions
• Update docs workflow to generate CLI docs before deploying

Usage

# Generate CLI docs
mise run docs:cli

# Check CLI docs are up to date (runs in CI)
mise run docs:cli:check

Notes

• CLI docs are auto-generated and should not be edited manually
• The check runs in CI when cmd/ or pkg/cli/ files change
• Docs include all commands, options, and examples from cobra definitions

Closes #1696

[tempusfrangit]

This looks fine but we should wire up mise to do some lifting for us!

[tempusfrangit]

@michaeldwan we'll want to track this for kong rewire.

[Copilot]

@bfirsh I've opened a new pull request, #2745, to work on those changes. Once the pull request is ready, I'll request review from you.

[tempusfrangit]

This seems reasonable. I'm certain once we move to Kong this will need to be reworked but that is just part of that migration.