ez switch should not claim to switch when it doesn't

[dezren39]

Problem

When the target branch is in a different worktree and the shell wrapper isn't active, ez switch prints "Switching to ..." but doesn't actually change the working directory. This is misleading.

Current behavior

• ez switch feat/x where feat/x is in a worktree
• Prints "Switching to feat/x" and a path
• User's shell stays in the original directory
• No indication that the switch didn't actually happen

Implemented fix (PR-C: feat/worktree-ops)

• Detects when shell wrapper isn't active
• Prints clear error message with manual cd instructions
• Exits with code 5 (usage error)
• Added --no-cd-required flag for scripts/agents that handle cd themselves (exits 0, prints path)

✗ Could not switch to `feat/x` — branch is checked out in a different worktree.
  Shell integration is not active (run `ez setup` to enable auto-cd).
  To switch manually, run:
  cd /path/to/.worktrees/feat-x

Related

• Upstream PR Unable to navigate in the stack tree #1 (worktree creation)
• PR-C: dezren39#2