chore(cloud-tasks): keep cloud runtime controls visible

[tatoalo]

Problem

Cloud tasks temporarily lose the selected model and reasoning controls after launch because the active session waits for preview configuration before rendering them

[trunk-io]

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 92f4c90.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: preserve cloud reasoning preview st..." | Re-trigger Greptile}

[stamphog]

Well-tested behavioral change to session config option seeding and merging logic, but it's T1d-complex with zero reviews and no ownership match — needs a team member to sign off before auto-approval.

[stamphog]

The two P1 bot findings are both resolved and well-tested in the current diff, but this is a complex behavioral change to core session service logic (130 lines in sessionService.ts, cloud config option seeding and merge paths) with no human team reviewer sign-off on the current head. Request a human review before auto-approving.