refactor(handlers): update all handlers for Echo v5 compatibility

Update all handler functions to use *echo.Context (pointer) instead of echo.Context (value) as required by Echo v5.

Changes across all handler files:
- analytics.go: Update handler signatures
- auth.go: Update authentication handler signatures
- book_matching.go: Update matching handler signatures
- collections.go: Update collection handler signatures
- collections_preview_test.go: Update test signatures
- commonhandlers.go: Update common handler signatures
- conflicts.go: Update conflict handler signatures
- context.go: Update context handler signatures
- dashboard.go: Update dashboard handler signatures
- devices.go: Update device handler signatures
- jobs.go: Update job handler signatures
- kobo.go: Update Kobo handler signatures
- koreader.go: Update Koreader handler signatures
- library.go: Update library handler signatures
- matching.go: Update matching handler signatures
- media.go: Update media handler signatures
- opds.go: Update OPDS handler signatures
- progress.go: Update progress handler signatures
- queue.go: Update queue handler signatures
- refresh_token.go: Update token handler signatures
- scanner.go: Update scanner handler signatures
- sidecar.go: Update sidecar handler signatures
- sync.go: Update sync handler signatures
- system_settings.go: Update settings handler signatures
- websocket.go: Update WebSocket handler signatures

All handlers now properly implement Echo v5's pointer-based context pattern.
This change is necessary for type safety and compatibility with Echo v5's
improved context handling and WebSocket support.

internal/handlers/context.go

@@ -4,12 +4,12 @@ import (
 	"bookhoard/internal/database"
 	"net/http"
 
-	"github.com/labstack/echo/v4"
+	"github.com/labstack/echo/v5"
 )
 
 // GetAuthenticatedUser safely retrieves the authenticated user from context
 // Returns an error if the user is not found in context or type assertion fails
-func GetAuthenticatedUser(c echo.Context) (database.Users, error) {
+func GetAuthenticatedUser(c *echo.Context) (database.Users, error) {
 	user, ok := c.Get("user").(database.Users)
 	if !ok {
 		return database.Users{}, echo.NewHTTPError(http.StatusInternalServerError, "authentication context error")
@@ -20,7 +20,7 @@ func GetAuthenticatedUser(c echo.Context) (database.Users, error) {
 // MustGetAuthenticatedUser gets user or panics
 // Only use this after authentication middleware has verified the user
 // Panicking here indicates a serious bug in the middleware chain
-func MustGetAuthenticatedUser(c echo.Context) database.Users {
+func MustGetAuthenticatedUser(c *echo.Context) database.Users {
 	user, err := GetAuthenticatedUser(c)
 	if err != nil {
 		panic(err) // Should never happen if authentication middleware is working correctly