chore: rename on-disk paths and env to vocagateway

[jatinkrmalik]

Summary

• Default data/config dirs are now ~/.local/share/vocagateway and ~/.config/vocagateway
• Env vars are VOCAGATEWAY_* only (no VOCAPHONE_* / Local Flow fallbacks)
• Model markers write/read .vocagateway-model.json
• WebUI localStorage keys moved to vocagateway.*

Stacked on #3. Intentional break while this is still pre-release.

Note for other developers

cc: @sesav @Mr-Sunglasses

If you already ran a gateway locally under the old names, move or recreate:

# Config + bootstrap token
mkdir -p ~/.config/vocagateway
mv ~/.config/vocaphone/token ~/.config/vocagateway/token 2>/dev/null || true
mv ~/.config/vocaphone/config.json ~/.config/vocagateway/config.json 2>/dev/null || true

# Data + downloaded models
mv ~/.local/share/vocaphone ~/.local/share/vocagateway 2>/dev/null || true

# Marker files inside models (otherwise installs look missing)
find ~/.local/share/vocagateway/models -name '.vocaphone-model.json' \
  -execdir mv {} .vocagateway-model.json \; 2>/dev/null || true

Also rename any VOCAPHONE_* env vars in your shell/systemd/compose to VOCAGATEWAY_*, and re-paste the token in the WebUI once (localStorage key changed).

CLI entry points (vocaphone-server, etc.) and the PyPI/extra name are unchanged in this PR.

Test plan

• Fresh start mints ~/.config/vocagateway/token and uses ~/.local/share/vocagateway
• VOCAGATEWAY_DATA_DIR / VOCAGATEWAY_MODELS_DIR overrides work
• Download a model; marker is .vocagateway-model.json
• Pairing / WebUI still auth with the new token path
• CI quality green