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/system_settings.go

@@ -6,7 +6,7 @@ import (
 	"strconv"
 
 	"github.com/jackc/pgx/v5"
-	"github.com/labstack/echo/v4"
+	"github.com/labstack/echo/v5"
 )
 
 type SystemSettingsHandler struct {
@@ -30,7 +30,7 @@ type ScanSettingsResponse struct {
 	Message                 string `json:"message,omitempty"`
 }
 
-func (h *SystemSettingsHandler) UpdateScanSettings(c echo.Context) error {
+func (h *SystemSettingsHandler) UpdateScanSettings(c *echo.Context) error {
 	var req UpdateScanSettingsRequest
 	if err := c.Bind(&req); err != nil {
 		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
@@ -71,7 +71,7 @@ func (h *SystemSettingsHandler) UpdateScanSettings(c echo.Context) error {
 	})
 }
 
-func (h *SystemSettingsHandler) GetScanSettings(c echo.Context) error {
+func (h *SystemSettingsHandler) GetScanSettings(c *echo.Context) error {
 	scanFrequencySetting, err := h.db.GetSystemSetting(c.Request().Context(), "scan_poll_interval_seconds")
 	if err != nil {
 		if err == pgx.ErrNoRows {