[v1.0] Add migration guides for Click, Typer, Cement, and argparse

[codeforester]

Goal

Give existing CLI maintainers a concrete, low-risk adoption path.

Scope

• Document incremental adoption around an existing Click or Typer command tree.
• Add recipes for configuration, lifecycle hooks, JSON/NDJSON output, diagnostics, history, and testing.
• Explain where base-cli differs from Cement, argparse, Cyclopts, and other alternatives.
• Include migration checklists, rollback guidance, and compatibility considerations.

Acceptance criteria

• Each targeted framework has a clear migration page with runnable examples.
• The guides identify features that remain owned by the underlying parser.
• A maintainer can adopt lifecycle features without rewriting commands.
• Links and examples are validated in CI.

Project fields

• Status: Backlog
• Priority: P2
• Area: Docs
• Initiative: Adoption Polish
• Size: M