Support local merge / stack collapse without GitHub

[dezren39]

Problem

ez merge only works through the GitHub API — it requires PRs to exist and merges them remotely. There is no way to:

• Locally merge a branch into its parent (like git merge --squash)
• Collapse a stack segment locally (merge multiple branches into one)
• Clean up finished branches from the stack without going through GitHub

This is limiting for local-only workflows, offline work, or when users want to squash a chain before pushing.

Current behavior

• ez merge calls GitHub's merge API; fails without a PR
• No local merge, squash, or fold operation
• Deleting a branch from the stack requires manual cleanup of stack.json

Proposed solution

1. ez merge --local — merge current branch into its parent locally (default: squash)
   • --strategy merge|squash|rebase to control merge method
   • Updates stack metadata: reparents children to the merged-into parent
   • Deletes the merged branch
2. ez fold (or ez collapse) — merge a contiguous range of branches into one
   • ez fold feat/a..feat/c squashes the range into a single branch
3. ez delete <branch> — remove a branch from the stack and reparent children
   • With --force to also delete the git branch

Use cases

• Local development before pushing anything
• Cleaning up experimental branches
• Squashing a chain of small fixup branches into one coherent change
• Offline workflows

[dezren39]

Implementation Update

Implemented in PR-E (feat/local-merge):

• ez merge --local — merge current branch into parent locally
  • --strategy squash (default): all commits → one squash commit
  • --strategy rebase: keep individual commits, rebase onto parent
  • --strategy merge: create merge commit (warns about restack conflicts, requires --force)
• ez merge --local --into <branch> — merge into a specific branch instead of parent
• ez fold <range> — fold a range of branches into one
  • ez fold feat/a..feat/c — squash range, survivor is bottom branch
  • ez fold feat/a..feat/c --name feat/combined — rename surviving branch
• Both commands reparent child branches and clean up worktrees
• Stack metadata updated automatically on merge/fold

PR: dezren39#4