useConnections() emits a growing partial list once per relay on subscribe

`useConnections()` seeds the stream with one emission per relay
(`src/lib/stores/useConnections.ts:22-31`):

```ts
const init = relays.map((relay) => { ... });

return rxNostr.createConnectionStateObservable().pipe(
startWith(...init),
scanLatestEach(({ from }) => from)
);
```

`startWith(...init)` spreads N relays as N separate emissions, and
`scanLatestEach` emits after each one. A subscriber therefore receives N values on
subscribe, each a growing partial list — `[a]`, `[a, b]`, `[a, b, c]` — rather than
one value holding the initial state.

`NostrApp` passes this straight to its default slot, so consumers rendering
`{#each connections as connection}` see the list fill in one relay at a time on
every subscribe.

Determined by code reading.

## Direction

Emit the initial state as a single value (`startWith(init)` with an accumulator that
takes a list, or seed the scan directly).

Start in src/lib/stores/useConnections.ts:22-31 and inspect how createConnectionStateObservable is combined with startWith and scanLatestEach. Verify the change by checking that a new subscriber receives one initial value containing all relay states, rather than one growing partial list per relay.

由索引模型根据 Issue 内容生成。