Add subgraph caching, proxy API, and indexer lag alerting

[Rickyy1017]

Summary

• Cache successful subgraph query responses in Redis with a configurable TTL and endpoint-specific cache namespace.
• Add authenticated typed proxy endpoints and a parallel aggregate endpoint.
• Expose metrics from the standalone indexer process, fix metric labels, scrape the worker, and alert when lag metrics disappear.
• Add focused cache/metric assertions and update operator/API documentation.

Verification

• Tests were not run, as requested.
• VS Code reports no TypeScript diagnostics in the changed TypeScript files.
• Compose config validation is blocked because .env.docker is absent; Compose also reports unset RABBITMQ_USER and RABBITMQ_PASS.

Closes #665
Closes #666
Closes #671
Closes #672

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