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>

jwt/cookies.go

@@ -6,7 +6,12 @@ import (
 	"time"
 )
 
-// Get the value of the access and refresh tokens
+// GetTokenCookies extracts access and refresh tokens from HTTP request cookies.
+// Returns empty strings for any cookies that don't exist.
+//
+// Returns:
+//   - acc: The access token value from the "access" cookie (empty if not found)
+//   - ref: The refresh token value from the "refresh" cookie (empty if not found)
 func GetTokenCookies(
 	r *http.Request,
 ) (acc string, ref string) {
@@ -25,7 +30,16 @@ func GetTokenCookies(
 	return accStr, refStr
 }
 
-// Set a token with the provided details
+// setToken is an internal helper that sets a token cookie with the specified parameters.
+// The cookie is HttpOnly for security and uses SameSite=Lax mode.
+//
+// Parameters:
+//   - w: HTTP response writer to set the cookie on
+//   - token: The token value to store in the cookie
+//   - scope: The cookie name ("access" or "refresh")
+//   - exp: Unix timestamp when the token expires
+//   - rememberme: If true, sets cookie expiration; if false, cookie is session-only
+//   - useSSL: If true, marks cookie as Secure (HTTPS only)
 func setToken(
 	w http.ResponseWriter,
 	token string,
@@ -48,7 +62,21 @@ func setToken(
 	http.SetCookie(w, tokenCookie)
 }
 
-// Generate new tokens for the subject and set them as cookies
+// SetTokenCookies generates new access and refresh tokens for a user and sets them as HTTP cookies.
+// This is a convenience function that combines token generation with cookie setting.
+// Cookies are HttpOnly and use SameSite=Lax for security.
+//
+// Parameters:
+//   - w: HTTP response writer to set cookies on
+//   - r: HTTP request (unused but kept for API consistency)
+//   - tokenGen: The TokenGenerator to use for creating tokens
+//   - subject: The user ID to generate tokens for
+//   - fresh: If true, marks the access token as fresh for sensitive operations
+//   - rememberMe: If true, tokens persist beyond browser session
+//   - useSSL: If true, marks cookies as Secure (HTTPS only)
+//
+// Returns an error if token generation fails. Cookies are only set if both tokens
+// are generated successfully.
 func SetTokenCookies(
 	w http.ResponseWriter,
 	r *http.Request,