docs(quartz): align tutorials with the layered patterns demoApp uses

The README's "Wiring relays into the store" tutorial used a
per-subscription SubscriptionListener.onEvent callback to feed the
store. EventCollector landed exactly to remove that boilerplate, so
update the example to register one connection-level collector at app
init and stop wiring listeners per subscribe() call.

The "Building a reactive feed UI" example showed project() ->
stateIn(WhileSubscribed) but never opened the relay subscription.
Bind it to the projection's collection lifecycle with .onStart {
client.subscribe } / .onCompletion { client.unsubscribe }, so the
relay subscription's lifetime equals the UI collector's. Also
demonstrate ProjectionState.filterItems for narrowing without a
re-query.

Drop the redundant client.connect() call from the wiring example
and add an explicit note (in both README and CLIENT) that
NostrClient connects on demand from subscribe()/publish() — connect()
is only useful after disconnect().

Other small fixes:
  - client.send(...) -> client.publish(...) (the actual API name).
  - Rename the variable from `observable` to `db` to match the demoApp
    code and the conceptual "this is the local database" framing.
  - Wrap the publish path in a viewModelScope.launch so the snippet
    is copy-pasteable into a ViewModel.

quartz/CLIENT.md

@@ -357,6 +357,8 @@ results.forEach { (relay, success) ->
 6. On disconnection, exponential backoff retries the connection
 7. On reconnection, filters are re-sent and events re-delivered
 
+`NostrClient` starts active by default and connects on demand — there's no need to call `client.connect()` at startup. That method only matters for resuming after a prior `disconnect()` (e.g., a user-toggled offline mode). Conversely, `client.disconnect()` is what you want when the app is going to background or being shut down: it tears down every socket and stops the auto-reconnect loop.
+
 ### Subscription Flow
 
 ```