Consolidate the fragile 3-RPC flow (suggestCommitAndBranch → createBranch +
checkout → runStackedAction) into a single server-side operation triggered by
`runStackedAction({ featureBranch: true })`. The server now generates the
branch name via AI, deduplicates it, creates + checks out the branch, then
runs the normal commit/push/PR pipeline atomically.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>