* fix(executors): forward X-Session-ID/X-Title agent metadata headers (port from 9router#2413)
Custom agent clients (e.g. non-OpenCode providers) commonly send X-Session-ID and X-Title headers for upstream request tracking/attribution, but forwardOpencodeClientHeaders() only forwarded x-opencode-* keys plus User-Agent, silently dropping these for every client. Extends the existing case-insensitive allowlist forwarding path with x-session-id/x-title.
Reported-by: Atikur Rahman Chitholian (@chitholian) (https://github.com/decolua/9router/issues/2413)
* chore(changelog): move #2413 entry to changelog.d fragment
Consistency with the repo's canonical changelog.d/fixes/ workflow (avoids
merge-storm re-conflicts from editing CHANGELOG.md directly).