Align user config directory settings filename with rooms.settings.yaml

[rosspeili]

Problem Statement

Settings search order uses rooms.settings.yaml in the current working directory, but user-level paths use a different name: %APPDATA%/rooms/settings.yaml (Windows) and ~/.config/rooms/settings.yaml (Unix). config init writes rooms.settings.yaml in cwd only. Users who copy their file to the config dir may use the wrong filename and wonder why settings are ignored.

Proposed Solution

Preferred (code + docs):

• Search both rooms.settings.yaml and legacy settings.yaml under the user config dir (document deprecation of the latter if kept).
• Optionally: config init --global writes to the user config dir using rooms.settings.yaml consistently.
• Update README, docs/ARCHITECTURE.md, and rooms/settings.py docstrings with a single table: path, filename, precedence.

Minimum: docs-only clarifying both names and precedence — if maintainers prefer a smaller first PR, split into docs PR then code PR (note in Additional Context).

Alternatives Considered

• Rename cwd file to settings.yaml everywhere — rejected; breaks existing feat: optional YAML settings, user profile, and config init/reset #28 docs and config init output.
• Only document cwd — rejected; power users expect XDG/AppData config to match project naming.

Priority

Medium 🟡

Additional Context

See settings_search_paths() and reset_settings_file() in rooms/settings.py. Reduces confusion after #28 without changing default “no file required” behavior.