test(infra): cover review-002 stream/PEM/cap error arms + drop dead WsTimeouts Default

- forward_stream build-error arm (forward.rs): wire-level test asserts
  one INVALID_INPUT envelope then stream end with zero upstream
  contact (a panicking responder counts as the contact guard), plus
  the from_jsonschema integration mirror (undeclared key + non-scalar
  placeholder, each naming its rejection source)
- PEM read-failure arms (http_client.rs): nonexistent CA path →
  CaBundleRead (sync new), nonexistent client-cert path → ClientCertRead
  (async reload, prior generation retained)
- Over-cap poll_write rejection leg (byte_adapter.rs): cap+1 write →
  InvalidData naming the cap; stream stays usable for an at-cap write
  afterwards
- SSE parser edges: CRLF split across feed chunks frames one line;
  invalid-UTF8 data lines drop without killing the frame stream
- from_value structural rejects: non-object doc, missing `info`,
  missing `paths`, non-object `paths` each name the member
- Connection-failure arms: accept-path ConnectionClosed →
  HandlerError::ConnectionClosed via stream_error_to_handler; read-pump
  demux-gone break ends the pump when the byte-stream side is dropped
- Delete the caller-less `impl Default for WsTimeouts` (the extension
  is constructed explicitly)

cargo llvm-cov --all-features: all named arms covered; TOTAL regions
94.18% (was 93.86%), lines 96.04% (was 95.77%); http_client.rs
86.56% lines (was 81.72%).

docs(tasks): mark review-002-fu-stream-error-coverage done

tasks/infra/review-002-fu-stream-error-coverage.md

@@ -1,7 +1,7 @@
 ---
 id: review-002-fu-stream-error-coverage
 name: Streaming error-arm coverage — forward_stream invalid input, PEM read-failure, over-cap poll_write mirror (post-bulk coverage gap)
-status: pending
+status: done
 depends_on: []
 scope: narrow
 risk: low