style(ux): simplify public registration flow

[selvalabs]

Summary

• simplify the public homepage around two clear paths: register an address or enter the member area
• clarify member access with phone plus private code
• improve the one-time access-code panel and focus it after registration
• ignore local .superpowers/ brainstorming artifacts

Validation

• uv run pytest tests/unit/test_web_home.py -q
• node --check src/monitor_comunitario/web/static/app.js
• uv run ruff check .
• uv run mypy src
• uv run pytest

Closes #56
Refs #25