## Stack context
This is the first PR in the V5 documentation stack. The migration guide and local-development wrapper build on it.
## What and why
Add Legacy and Latest versions to the API Reference navigation, organize all V5 operations by user workflow, and introduce concise overview pages for each domain. The Latest reference consumes the authoritative `/v5/openapi` document published by the Mono API stack.
```mermaid
flowchart LR
Legacy[Legacy V3/V4 OpenAPI] --> Selector[Reference version selector]
V5[V5 OpenAPI] --> Selector
Selector --> Pages[Version-specific endpoint pages]
```
The `GET /ns` compatibility alias remains in the OpenAPI document but is intentionally omitted from navigation in favor of `GET /namespaces`.
## Validation
- Parsed `docs.json` successfully with `jq`.
- Compared navigation against the generated V5 schema: 22 displayed operations, 23 schema operations, with only `GET /ns` intentionally omitted.
- Mintlify build validation passed against the local generated V5 OpenAPI snapshot.
## Deployment dependency
The committed source is `https://api.supermemory.ai/v5/openapi`, which returns 404 until Mono PR #3306 and its API stack are deployed. Merge this PR after that endpoint is live.
