[indexer/verifier] Add V0 persistence layer for observations and reports

[FlowmemoryAI]

Objective

Design and implement a local V0 persistence layer for FlowMemory observations, pulses, rootfields, and verifier reports.

Allowed folders

• services/indexer/
• services/verifier/
• services/api/
• services/shared/
• docs/
• research/indexer-verifier/
• package.json only for service scripts if needed

Forbidden folders

• contracts/
• hardware/
• apps/
• chain/L1 implementation
• tokenomics
• production deployment config
• production database deployment

Acceptance criteria

• Defines the V0 storage model for observations, pulses, rootfields, reports, duplicate markers, and reorg markers.
• Uses local development storage only, such as a file-backed store or SQLite if approved in the issue work.
• Adds fixture-backed persistence tests.
• API can read persisted demo state without changing endpoint shapes.
• No production DB deployment, secrets, RPC keys, migrations for production infra, tokenomics, or proof network.

Risk level

Medium

Recommended agent

FlowMemory Indexer / Verifier / API Agent