Remove outdated rejection of targeted messages in 1:1 chats

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## Description

`@microsoft/teams.apps` rejects targeted messages in personal chats with:

```
Targeted messages are not supported in 1:1 (personal) chats.
```

Teams does support targeted messages in 1:1 chats, so this validation is out of date and prevents otherwise valid sends.

## Reproduction

Using `@microsoft/teams.apps@2.0.15`:

1. Handle an inbound activity in a conversation whose `conversationType` is `personal` and whose recipient has `isTargeted: true`.
2. Call `ActivityContext.send()` with an ordinary message that has no explicit recipient.
3. `ActivityContext.shouldOutboundBeAutoTargeted()` applies the initiating user as the targeted recipient.
4. `ActivitySender.send()` detects both `recipient.isTargeted === true` and `conversationType === 'personal'`, then throws before calling the conversations API.

The relevant guard is in `packages/apps/src/activity-sender.ts`:

```ts
if (isTargeted && ref.conversation.conversationType === 'personal') {
throw new Error('Targeted messages are not supported in 1:1 (personal) chats.');
}
```

## Expected behavior

The SDK should send the targeted activity in a 1:1 conversation through the targeted activity API, just as it does for other supported conversation types.

## Actual behavior

The SDK throws locally and never attempts the API request.

## Additional context

This can also happen unexpectedly when application code sends an ordinary message: the SDK's inbound-target propagation adds `isTargeted: true`, after which `ActivitySender` rejects the resulting personal-chat message. Removing the outdated personal-chat guard should allow the existing targeted create/update path to handle it.

Start in packages/apps/src/activity-sender.ts at the guard that rejects targeted messages when conversationType is personal, then trace the existing targeted create/update path used for other conversation types. Verify that a targeted activity in a personal conversation reaches the conversations API instead of throwing locally, including the inbound-target propagation case described in the issue.

Written by the indexing model from the issue text.