## Why

`TickerService` exposes `start()` and `stop()` to ordinary consumers even though the current Nenjim architecture makes the Hub the lifecycle owner and models active implementations separately through `NenjimProcess`. This leaks process control through a domain service API and promises a stop lifecycle that the canonical process contract does not support.

## What Changes

- **BREAKING**: Remove `start()` and `stop()` from the public `TickerService` contract.
- Keep `TickerServiceImpl` as both the lifecycle-free service view and the Hub-started `NenjimProcess` view.
- Remove the implementation's public general stop operation while retaining private rollback that stops every `PriceSource` started during a failed startup attempt.
- Keep `PriceSource` lifecycle contracts, latest-price behavior, persistence, Registry resolution, and Hub startup wiring unchanged.
- Update the canonical Ticker specification, JavaDoc, and Nenjim documentation to describe Hub-owned lifecycle.

## Capabilities

### Modified Capabilities

- `assetaz-ticker-service`: Separates the ordinary latest-price service API from Hub-owned process startup and limits source stopping to failed-start cleanup.

## Impact

- Changes the public `com.r35157.assetaz.services.ticker.TickerService` source contract and the public methods of `TickerServiceImpl`.
- Existing callers must stop invoking Ticker lifecycle through the service view; the Hub continues to invoke startup through `NenjimProcess`.
- Adds no common stop/restart support, shutdown orchestration, source lifecycle changes, dependencies, or automated tests.