docs(reference): add rc command reference

[cxymds]

Summary

• Add an English docs/reference/rc/ command reference for all top-level rc operations.
• Follow the MinIO mc reference style with Purpose, Syntax, Parameters, Examples, and Behavior sections while keeping content specific to rc.
• Document preferred noun-first commands and legacy-compatible command forms for migration clarity.

Background

The project had CLI behavior documentation in docs/SPEC.md and examples in README.md, but did not have a MinIO-style operation reference for the supported rc command surface. This PR adds standalone user-facing reference pages without changing CLI contracts.

Solution

Each operation exposed by rc --help now has a Markdown page under docs/reference/rc/. The overview page links the command families and explains remote path format, output modes, and credential setup.

Test Status

• Markdown-only documentation change; Rust compile/lint/test checks skipped per project docs exception.
• Ran a Node verification script over 30 Markdown files to check:
  • no CJK text in reference docs
  • no TODO/TBD/FIXME placeholders
  • no MinIO RST :mc roles left behind
  • all local Markdown links resolve

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