Rewrite Chainlink as a minimal account synchronization service

@bmuddha is already working on this.

Since Sep 17, 2026.

### Goal

Replace Chainlink with a smaller account synchronization service that is easier to operate.

### Why

Account synchronization is critical infrastructure, but its responsibilities should be narrow and predictable. A smaller service should reduce operational complexity and make failure behavior and reliability boundaries easier to understand.

### Scope

- Define the service's minimal responsibilities and public contract, moving unrelated responsibilities to their owning components.
- Preserve the account states and update guarantees required by validator workflows.
- Make startup, catch-up, reconnect, and restart behavior explicit and recoverable.
- Provide health signals, back-pressure behavior, and actionable failure reporting.
- Provide compatibility and migration paths for existing deployments, including a tested rollback path.
- Qualify correctness and sustained operation under realistic load.

Completion requires the service to pass correctness and load qualification and replace the current implementation through the tested migration and rollback path.

Begin after Validator V3's network-integrity work and run alongside the staged Committor refactor. Prioritize this work over SDK V1 when capacity is constrained.

Related planning: magicblock-labs/dev-kanban#193.