fix(cli): push per-task branch to origin before creating PR; drop dead autoCreatePr

In PR-mode, processPullRequestMergeTask called gh pr create --head
fusion/<task-id> without ever pushing the branch to origin. PR creation
failed and the task stalled in in-review — and combined with the
recover-mergeable-review sweep bug, the stalled task got force-merged
locally instead. Push the branch via git push -u origin <branch>
immediately before createPr (skipped when an existing PR already covers
the branch).

Also remove the dead autoCreatePr setting: defined as a default in the
schema and Settings type but never read anywhere.

Related to https://github.com/Runfusion/Fusion/issues/21

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/src/settings-schema.ts

@@ -139,7 +139,6 @@ export const DEFAULT_PROJECT_SETTINGS = {
   autoArchiveDoneAfterMs: 48 * 60 * 60 * 1000,
   archiveAgentLogMode: "compact",
   autoUpdatePrStatus: false,
-  autoCreatePr: false,
   githubCommentOnDone: false,
   githubCommentTemplate: undefined,
   autoBackupEnabled: false,