Refactor database interface to use *sql.DB directly

Simplified the database layer by removing custom interface wrappers
and using standard library *sql.DB and *sql.Tx types directly.

Changes:
- Removed DBConnection and DBTransaction interfaces from database.go
- Removed NewDBConnection() wrapper function
- Updated TokenGenerator to use *sql.DB instead of DBConnection
- Updated all validation and revocation methods to accept *sql.Tx
- Updated TableManager to work with *sql.DB directly
- Updated all tests to use db.Begin() instead of custom wrappers
- Fixed GeneratorConfig.DB field (was DBConn)
- Updated documentation in doc.go with correct API usage

Benefits:
- Simpler API with fewer abstractions
- Works directly with database/sql standard library
- Compatible with GORM (via gormDB.DB()) and Bun (share same *sql.DB)
- Easier to understand and maintain
- No unnecessary wrapper layers

Breaking changes:
- GeneratorConfig.DBConn renamed to GeneratorConfig.DB
- Removed NewDBConnection() function - pass *sql.DB directly
- ValidateAccess/ValidateRefresh now accept *sql.Tx instead of DBTransaction
- Token.Revoke/CheckNotRevoked now accept *sql.Tx instead of DBTransaction

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

hwsauth/authenticate.go

@@ -1,7 +1,6 @@
 package hwsauth
 
 import (
-	"database/sql"
 	"net/http"
 	"time"
 
@@ -11,14 +10,14 @@ import (
 
 // Check the cookies for token strings and attempt to authenticate them
 func (auth *Authenticator[T]) getAuthenticatedUser(
-	tx *sql.Tx,
+	tx DBTransaction,
 	w http.ResponseWriter,
 	r *http.Request,
-) (*authenticatedModel[T], error) {
+) (authenticatedModel[T], error) {
 	// Get token strings from cookies
 	atStr, rtStr := jwt.GetTokenCookies(r)
 	if atStr == "" && rtStr == "" {
-		return nil, errors.New("No token strings provided")
+		return authenticatedModel[T]{}, errors.New("No token strings provided")
 	}
 	// Attempt to parse the access token
 	aT, err := auth.tokenGenerator.ValidateAccess(tx, atStr)
@@ -26,29 +25,29 @@ func (auth *Authenticator[T]) getAuthenticatedUser(
 		// Access token invalid, attempt to parse refresh token
 		rT, err := auth.tokenGenerator.ValidateRefresh(tx, rtStr)
 		if err != nil {
-			return nil, errors.Wrap(err, "auth.tokenGenerator.ValidateRefresh")
+			return authenticatedModel[T]{}, errors.Wrap(err, "auth.tokenGenerator.ValidateRefresh")
 		}
 		// Refresh token valid, attempt to get a new token pair
 		model, err := auth.refreshAuthTokens(tx, w, r, rT)
 		if err != nil {
-			return nil, errors.Wrap(err, "auth.refreshAuthTokens")
+			return authenticatedModel[T]{}, errors.Wrap(err, "auth.refreshAuthTokens")
 		}
 		// New token pair sent, return the authorized user
 		authUser := authenticatedModel[T]{
 			model: model,
 			fresh: time.Now().Unix(),
 		}
-		return &authUser, nil
+		return authUser, nil
 	}
 
 	// Access token valid
 	model, err := auth.load(tx, aT.SUB)
 	if err != nil {
-		return nil, errors.Wrap(err, "auth.load")
+		return authenticatedModel[T]{}, errors.Wrap(err, "auth.load")
 	}
 	authUser := authenticatedModel[T]{
 		model: model,
 		fresh: aT.Fresh,
 	}
-	return &authUser, nil
+	return authUser, nil
 }