serverless-schema-management updateSchema bypasses handleSchemaError

## Problem

`updateSchema` in `src/services/serverless-schema-management.service.ts` has its own inline error handler (lines 347-356) that does not call `handleSchemaError`. It uses `JSON.stringify(error.response.data)` instead of extracting the human-readable message.

All other methods in this service correctly delegate to `handleSchemaError`, which extracts `data.message`, `data.error`, plain-text strings, etc.

## Expected behavior

`updateSchema` should delegate to `handleSchemaError` like the other methods, so Cloud Serverless `{"code":"...","message":"..."}` errors are surfaced as readable messages instead of raw JSON blobs.

## Affected code

`src/services/serverless-schema-management.service.ts` lines 347-356 (inline catch in `updateSchema`)

Compare with `handleSchemaError` at line 362 which correctly handles all error formats.

## Context

Found during error handling audit in PR #31.

Read src/services/serverless-schema-management.service.ts, starting with the inline catch in updateSchema at lines 347-356 and then handleSchemaError at line 362. Compare updateSchema with the other methods in the service. Done means Cloud Serverless errors containing code and message are surfaced as readable messages rather than raw JSON blobs.

Written by the indexing model from the issue text.