feat: write v2 LLMO config to Aurora

[aniham]

depends on: https://github.com/adobe/mysticat-data-service/pull/135

feat: Migrate V2 LLMO customer config from S3 to PostgreSQL (Aurora)

Summary

Moves V2 customer configuration storage from S3 to PostgreSQL (Aurora) and syncs brands to the Postgres brands table. This replaces the previous S3-based storage and dual-write setup with a single Postgres source of truth.

Changes

Storage layer

• customer-config-v2-storage.js – New module for reading and writing V2 customer config in the llmo_customer_config table via PostgREST
• brand-presence-sync.js – Syncs brands from customer config into the Postgres brands table on config save/patch

Brands controller

• Switches from llmoConfig.readCustomerConfigV2 / writeCustomerConfigV2 (S3) to readCustomerConfigV2FromPostgres / writeCustomerConfigV2ToPostgres
• Adds requirePostgrestForV2Config() – returns 503 when Postgres is unavailable (DATA_SERVICE_PROVIDER != postgres)
• All config endpoints (getCustomerConfig, getCustomerConfigLean, getTopics, getPrompts, saveCustomerConfig, patchCustomerConfig) now use Postgres

Behavior

• 503 Service Unavailable when Postgres is not configured
• 404 when config is missing (unchanged)
• Brand sync runs on every save/patch (no conditional dual-write)

Requirements

• DATA_SERVICE_PROVIDER=postgres for V2 config endpoints
• llmo_customer_config table with organization_id, config, updated_by
• brands table for brand sync

Testing

• Unit tests for customer-config-v2-storage and brand-presence-sync
• Brands controller tests updated for Postgres storage
• 503 tests added for all config endpoints when Postgres is unavailable, with full branch coverage

Documentation

• docs/reference/llmo-brand-presence-schema-and-v2-config-writeup.md – schema and behavior notes

[github-actions]

This PR will trigger a minor release when merged.

[codecov]

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