* Fix all golangci-lint issues across the codebase
Resolve 77 lint issues reported by golangci-lint with gocritic, gocognit,
gocyclo, maintidx, dupl, mnd, unparam, ireturn, goconst, and errcheck
enabled. Net reduction of ~175 lines through shared helpers and
deduplication.
* Suppress staticcheck SA1019 for intentional deprecated field usage
The Storage.Path field is deprecated but still read for backwards
compatibility with existing configs that haven't migrated to the URL field.
Replace raw database/sql with jmoiron/sqlx for cleaner query handling.
Support both SQLite (default) and PostgreSQL as configurable backends.
Configuration via:
- CLI flags: -database-driver, -database-path, -database-url
- Environment: PROXY_DATABASE_DRIVER, PROXY_DATABASE_PATH, PROXY_DATABASE_URL
- Config file: database.driver, database.path, database.url
Tests run against both databases when PROXY_DATABASE_URL is set.