feat: Add initiative review gate before push

When all phases complete, the initiative now transitions to
pending_review status instead of silently stopping. The user
reviews the full initiative diff and chooses:
- Push Branch: push cw/<name> to remote for PR workflows
- Merge & Push: merge into default branch and push

Changes:
- Schema: Add pending_review to initiative status enum
- BranchManager: Add pushBranch port + SimpleGit adapter
- Events: initiative:pending_review, initiative:review_approved
- Orchestrator: checkInitiativeCompletion + approveInitiative
- tRPC: getInitiativeReviewDiff, getInitiativeReviewCommits,
  getInitiativeCommitDiff, approveInitiativeReview
- Frontend: InitiativeReview component in ReviewTab
- Subscriptions: Add initiative events + missing preview/conversation
  event types and subscription procedures

apps/server/git/branch-manager.ts

@@ -56,4 +56,10 @@ export interface BranchManager {
    * Get the raw unified diff for a single commit.
    */
   diffCommit(repoPath: string, commitHash: string): Promise<string>;
+
+  /**
+   * Push a branch to a remote.
+   * Defaults to 'origin' if no remote specified.
+   */
+  pushBranch(repoPath: string, branch: string, remote?: string): Promise<void>;
 }