neutralize upstream service branding

docs/superpowers/specs/2026-06-12-upstream-brand-neutralization-design.md

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+# Upstream Brand Neutralization Design
+
+## Goal
+
+Remove the upstream product name from the current Memory Gateway working tree while preserving the upstream HTTP protocol and application behavior.
+
+## Scope
+
+- Rename the upstream client module, class, configuration fields, environment variables, state attributes, response fields, tests, and integration test file to neutral `backend` terminology.
+- Rewrite README, Skill documentation, examples, package metadata, and test records to describe an "upstream memory service".
+- Remove the upstream-specific environment example because its variable names identify the product.
+- Preserve `/api/v1/memory/add`, `/api/v1/memory/flush`, and `/api/v1/memory/search` paths.
+- Do not rewrite Git history.
+
+## Compatibility
+
+This is an intentional configuration and response-schema rename. Deployments must move to `MEMORY_GATEWAY_BACKEND_*` variables, and health/add/flush consumers must read the `backend` field. No legacy aliases are retained because they would defeat the neutralization requirement.
+
+## Verification
+
+- Add an automated repository scan that rejects the forbidden upstream token in current files and file names.
+- Run the full unit suite and compilation checks.
+- Run a final case-insensitive repository scan excluding `.git`, virtual environments, runtime data, and generated bytecode.