Exception in the prompt AsyncIterable is swallowed at debug level and query() hangs forever

## Symptom

If the `AsyncIterable` passed as `prompt=` to `query()` raises — a bug in the caller's generator, or a message that fails `json.dumps` — the exception is logged at **debug** level and discarded. Stdin stays open, the CLI keeps waiting for input that will never arrive, no result is ever produced, and `query()` blocks forever. There is no error, no timeout, nothing — from the caller's perspective the SDK just stops.

## Mechanism

`Query.stream_input` (`src/claude_agent_sdk/_internal/query.py:829`):

```python
try:
async for message in stream:
if self._closed:
break
await self.transport.write(json.dumps(message) + "\n")

await self.wait_for_result_and_end_input()
except Exception as e:
logger.debug(f"Error streaming input: {e}")
```

On any exception the task exits without calling `end_input()` and without telling anyone. The consumer is blocked in `receive_messages()`; the CLI is blocked on stdin; neither side can make progress.

## Repro (real CLI, SDK 0.2.116, CLI 2.1.207)

Two variants, both verified against the live CLI with a 45s watchdog:

- Generator raises **before yielding anything** → `query()` yields 0 messages and hangs until the watchdog kills it (would hang forever otherwise).
- Generator yields one valid message, first turn completes normally (assistant + result arrive), then raises → `query()` hangs after the healthy-looking turn.

In both cases the only trace of the `ValueError` is an invisible debug log line.

## Suggested fix

Outside teardown (`self._closed`), the failure should: log at error level, close stdin (`end_input()`) so the CLI can wind down, and push an `{"type": "error"}` message into the message stream — the same mechanism `_read_messages` already uses — so `receive_messages()` raises promptly.

PR incoming with this fix + a regression test (fails on main via bounded timeout, passes with the fix). After the fix, both real-CLI repros above raise `Error streaming input: ...` within seconds instead of hanging.