2.80.0

(feat): Add opt-in allow-user-agent-app-info config. When enabled, generated clients expose an optional AppInfo client option (Name, Version?, Comment?) whose sanitized product token is appended to whatever User-Agent the SDK would otherwise send ({sdk}/{version} ... {product}/{product-version} ({comment})), following RFC 9110. Disabled by default, so existing generated output is byte-identical, and it composes with include-platform-headers, the configured user-agent template value, and the user-agent-name-from-package fallback. Caller-supplied values are trimmed and encoded (name/version percent-encoded to RFC 7230 tchar; comment delimiters (, ), \ and control characters incl. CR/LF escaped), so untrusted values cannot inject header content. Still overridable by an explicit User-Agent header and suppressed by omit-fern-headers. Works in both unified and non-unified client-options modes; generated code compiles for net462, net8.0, and netstandard2.0.