feat(cli): add global config and multi-inbox support

[spignotti]

What changed

• move default config and runtime files to the XDG-style config directory
• add interactive renamr init setup for inbox path, language, and model
• support multiple configured inboxes plus a single-inbox CLI override
• inject configured language into metadata extraction and add English month parsing
• update README examples and remove the unused environment settings module
• harden init output/ordering and date parsing edge cases

Why

renamr v2 is intended to work as a globally installed CLI instead of a current-directory tool, while also supporting multi-inbox workflows and configurable output language.

Validation

• nox passed (lint, pyright, pytest)
• manual smoke check of renamr init --config ...
• manual check that invalid matched dates now return None instead of raising