…ndling (microsoft#635)

## Summary

Ports two merged **teams.py** PRs to TypeScript:

- microsoft/teams.py#453 — streaming error handling for the 2-minute
timeout & "content stream not allowed"
- microsoft/teams.py#495 — support resetting response streams (reuse
after `close()`)

## Streaming error handling (port of microsoft#453)

- Add `TerminalStreamError`, `StreamTimedOutError`, and
`StreamNotAllowedError` (in `types/streamer.ts`).
- `HttpStream.send()` now inspects the `403` response body and maps it
to the right error instead of always treating a `403` as canceled:
  - `exceeded streaming time` → `StreamTimedOutError` (marks `timedOut`)
  - `cancel` → `StreamCancelledError`
  - `not allowed` → `StreamNotAllowedError`
  - anything else / empty body → `TerminalStreamError`
- On a 2-minute streaming timeout, the stream finalizes by **updating
the original message in place** — it drops the `streaminfo` entity and
stream `channelData` so the send routes through *update* (reusing the
id) rather than posting a duplicate.
- Chunk sends swallow a timeout mid-stream; `close()` then sends the
buffered content as a plain final message.
- `retry` gains a `nonRetryable` option so terminal stream errors are
not retried.

## Reusable streams (port of microsoft#495)

- Emitting or updating after `close()` reopens the stream on the **same
instance**, starting a new streamed message.
- `close()` is idempotent until the next emit/update.
- `app.process.ts` close listener switched from `once` → `on` so each
reused-stream close fires.

## Example

Adds `examples/stream`, mirroring the teams.py example's final state:

- default message → single-stream demo with suggested actions
- `simple-card` → sends a minimal Adaptive Card outside the streaming
flow
- `multi-stream` → emits an Adaptive Card as stream 1's final message,
`close()`s, then reuses `ctx.stream` for a second streamed response

## Tests

- `packages/apps` http-stream spec extended: 403 message→error mapping
(parametrized), empty-body 403 → terminal error, final-send timeout
updates in place, mid-stream timeout updates in place, and
emit-after-close stream reuse.
- Full `packages/apps` suite passes (294 tests); `tsc` and eslint clean
across the changed library files and the new example.

## Notes

- The Python-only `uv.lock` change was not ported.
- `examples/stream/.env` is gitignored (no credentials committed).

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Co-authored-by: Copilot <[email protected]>
Co-authored-by: Copilot Autofix powered by AI <[email protected]>