Hot reload for worker runtime parameters

### Problem

Worker runtime parameters are currently read at startup only. In practice, changes to scheduling interval, concurrency, timeout, retry, and rate-limit settings usually require a worker restart to take effect. That adds operational overhead and makes online tuning harder.

### Request

Support hot reload for worker runtime parameters so configuration changes can take effect without restarting workers.

### Suggested scope

- Runtime knobs: `poll_interval`, `claim_batch_size`, `deadline_duration`, `priority_aging_interval`, concurrency, rate limiting, and similar settings.
- Declarative worker-owned business config: include it if it is safe to update online.

### Out of scope

- Task code
- Execution logic
- One-off task inputs

Start by tracing where workers read poll_interval, claim_batch_size, deadline_duration, priority_aging_interval, concurrency, rate limiting, and related settings. Determine how configuration changes could reach running workers and which declarative business configuration is safe to update online; done means supported runtime changes take effect without a restart, while task code and one-off inputs remain unchanged.

Written by the indexing model from the issue text.