Tighten how server URL values are emitted in the server-urls template so
that spec-supplied text is always serialized into a proper Go context:

- Route server descriptions and URLs through stripNewLines when they are
  written into generated // comments, so a multi-line value stays on the
  comment line instead of spilling into following lines.
- Emit server URL and variable-default values via toGoString (now backed
  by strconv.Quote) instead of hand-wrapping them in quotes, so quotes,
  backslashes, and newlines are escaped correctly.
- Harden StringToGoString to use strconv.Quote; the previous version only
  escaped double quotes and mishandled backslashes. This also tidies up
  the content-type literals that already used it.
- Extend stripNewLines to drop carriage returns as well as newlines.

Add regression tests covering the server-urls rendering and the
StringToGoString escaping, and confirm `make generate` produces no
changes to committed output.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Spec-derived paths and string enum values were interpolated into generated
Go source without escaping, so a value containing a quote could produce
malformed output. Route paths in the server registration templates and
string enum constants are now emitted through strconv.Quote (the existing
toGoString helper) so they are always valid, properly-escaped Go string
literals. Generated output is unchanged for normal specs.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>