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/library.go

@@ -3,7 +3,7 @@ package router
 import (
 	"bookhoard/internal/handlers"
 
-	"github.com/labstack/echo/v4"
+	"github.com/labstack/echo/v5"
 )
 
 func registerLibraryRoutes(cfg *Config) {
@@ -36,7 +36,7 @@ func registerLibraryRoutes(cfg *Config) {
 	adminLibrary.GET("/:id/folders", cfg.LibraryHandler.GetLibraryFolders)
 	adminLibrary.DELETE("/:id/folders", cfg.LibraryHandler.DeleteLibraryFolder)
 	adminLibrary.GET("/:id/stats", cfg.LibraryHandler.GetLibraryStats)
-	adminLibrary.POST("/:id/scan", func(c echo.Context) error {
+	adminLibrary.POST("/:id/scan", func(c *echo.Context) error {
 		libraryID := c.Param("id")
 		scanReq := map[string]interface{}{
 			"library_id": libraryID,
@@ -44,7 +44,7 @@ func registerLibraryRoutes(cfg *Config) {
 		c.Set("scan_request", scanReq)
 		return h.ScanLibrary(c)
 	})
-	adminLibrary.GET("/:id/media-items", func(c echo.Context) error {
+	adminLibrary.GET("/:id/media-items", func(c *echo.Context) error {
 		libraryID := c.Param("id")
 		c.QueryParams().Set("library_id", libraryID)
 		return cfg.MediaHandler.ListMediaItems(c)