Adds a tabbed UI with single-contact form and CSV upload. Users can
download a sample CSV, upload their file, and get partial import with
per-row error reporting. Enrichment jobs enqueue for each imported contact.
Rename all modules, functions, variables, routes, and UI text from
qso/qsos to contact/contacts. Database table stays as "qsos" to avoid
migration. Add /qsos -> /contacts redirects for old URLs.
Maidenhead grid module converts grid squares to lat/lon coordinates.
Submission form validates grids, bands, modes, and email, computes
positions and distance, then triggers the weather/HRRR/terrain
processing pipeline via Oban.
