fix the content codings announced on the stream

fix the content codings announced on the stream

Three inconsistencies between what the headers promised and what went
out on the socket:

- headers_render() announced "Content-Encoding: chunked" on every
  streaming response the client had not asked to compress. chunked is a
  transfer coding, not a content coding. Apache rewrote the response and
  it went unnoticed; nginx forwards the header as it stands, and a
  browser that meets a content coding it does not know refuses the whole
  body. Transfer-Encoding: chunked, right below, already says it.

- the deflate stream was built without stating the window, and the
  filter then emits raw deflate, while Content-Encoding: deflate
  promises the zlib wrapper of RFC 1950. Whoever asked for deflate got
  bytes that could not be inflated as announced.

- get_encoding() compared the tokens of Accept-Encoding as they came out
  of explode(), with their leading space and their quality attached.
  "gzip, deflate, br" only ever matched its first token, and a coding
  refused with q=0 was taken as accepted.

Checked on the daemon socket, reading the raw stream and inflating it:
gzip and deflate both come out whole across several chunks, every chunk
self contained, the blocks paired and nothing duplicated; with no
Accept-Encoding no Content-Encoding is sent at all.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014M1jiEq9cHdE5SE5j6vFuE