refactor(router): update routes and middleware for Echo v5

Update all router files to use Echo v5 APIs and type signatures.

Changes in router.go:
- Replace echomiddleware.Logger() with RequestLogger() (line 144)
- Update import from echo/v4 to echo/v5

Changes in frontend.go:
- Update frontend handler signatures to use *echo.Context
- Fix middleware registration for v5 compatibility

Changes in auth.go, library.go, scanner.go, sync.go, helpers.go:
- Update handler function signatures to *echo.Context
- Ensure consistent type usage across all route handlers

All routes now properly implement Echo v5's middleware and handler patterns.

internal/router/helpers.go

@@ -9,10 +9,10 @@ import (
 	"github.com/google/uuid"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
-	"github.com/labstack/echo/v4"
+	"github.com/labstack/echo/v5"
 )
 
-func getTemplateUserWithTheme(c echo.Context, cfg *Config) (templates.User, error) {
+func getTemplateUserWithTheme(c *echo.Context, cfg *Config) (templates.User, error) {
 	userID := c.Get("user_id").(string)
 	userEmail := c.Get("user_email").(string)
 	userUsername := c.Get("user_username").(string)