Fix mistakenly encoding cookies to proxy

We use the cookie parser to remove the code-server token but by default
it encodes using encodeURIComponent, which encodes more than is strictly
necessary and can break proxied applications.

Now we pass the cookies through unchanged (other than removing the
code-server token).

Fixes #7927.

CHANGELOG.md

@@ -22,6 +22,12 @@ Code v99.99.999
 
 ## Unreleased
 
+### Fixed
+
+- When proxying, cookies were being decoded and re-encoded, which could cause
+  issues for applications that encode differently. Cookies are now passed
+  through unchanged (aside from stripping out code-server's session token).
+
 ## [4.131.0](https://github.com/coder/code-server/releases/tag/v4.131.0) - 2026-07-30
 
 Code v1.131.0