refactor: remove unnecessary type conversions and handle ignored errors across codebase

Remove redundant type conversions that Go 1.26 makes unnecessary or that
were already no-ops:

- uuid.UUID(x.Bytes) → x.Bytes (uuid.UUID is [16]byte, same as pgtype UUID Bytes)
- pgtype.UUID{Bytes: [16]byte(u), Valid: true} → pgtype.UUID{Bytes: u, Valid: true}
- (*time.Time)(&x.Time) → &x.Time
- json.RawMessage(x) → x where x is already []byte
- []byte(stringVal) → stringVal where []byte is expected
- int()/int64()/byte() casts on values already of the target type
- Decompressor(fn) → fn (type is identical)

Handle previously ignored error returns:

- collections.go: check json.Unmarshal error in GetCollection
- conversion_service.go: check fileSize.Scan() error
- app_test.go: check app.Shutdown() error in benchmark

internal/handlers/filters.go

@@ -77,7 +77,7 @@ func (h *FiltersHandler) GetSavedFilters(c *echo.Context) error {
 			ID:           uuid.Must(uuid.FromBytes(f.ID.Bytes[:])),
 			Name:         f.Name,
 			ResourceType: f.ResourceType,
-			Filters:      json.RawMessage(f.Filters), // Return JSONB as-is
+			Filters:      f.Filters,
 			CreatedAt:    f.CreatedAt.Time.Format(time.RFC3339),
 			UpdatedAt:    f.UpdatedAt.Time.Format(time.RFC3339),
 		}