fix(cmd): detach worktrees before pool reuse

[kunchenguid]

Summary

• Detach worktrees when acquiring and returning them so dirty or branch-checked-out trees can be safely reset for reuse.
• Make treehouse return --force recover conflicted or dirty worktrees through forced cleanup instead of failing before reset.
• Update README and CLI help text to make the destructive --force cleanup behavior explicit, with e2e coverage for the detach and forced-return cases.

Risk Assessment

✅ Low: The change is narrowly scoped to detaching worktree HEADs before reuse/return and adds focused regression coverage, with no material issues found in the changed code.

Testing

• Summary: Exercised the new dirty-worktree detach regressions plus the full Go test suite; all tests passed.
• go test ./cmd
• go test ./cmd -run 'Test(GetDetachesWorktreeWhenLeavingDirty|ReturnForceCleansAndDetachesCheckedOutBranch|ReturnForceCleansConflictedWorktree)$' -count=1
• go test ./... -count=1
• Outcome: ✅ passed across 1 run (28.6s)

Pipeline

Updates from git push no-mistakes

✅ **Rebase** - passed

Round 1 - passed ✅

🔧 **Review** - 1 issue found → auto-fixed

Round 1 - found 1 error

• 🚨 cmd/return_cmd.go:47 - treehouse return --force now runs a non-forced git checkout --detach before cleanup. A dirty worktree with an unmerged/conflicted index can make this detach fail before pool.Release reaches ResetWorktree's forced checkout/reset, so --force can no longer recover and clean that state. Move the detach until after the non-force confirmation, or let the forced reset path handle detaching for --force.

Round 2 (auto-fix) - passed ✅

✅ **Test** - passed

Round 1 - passed ✅

• go test ./cmd
• go test ./cmd -run 'Test(GetDetachesWorktreeWhenLeavingDirty|ReturnForceCleansAndDetachesCheckedOutBranch|ReturnForceCleansConflictedWorktree)$' -count=1
• go test ./... -count=1

🔧 **Document** - 1 issue found → auto-fixed (2)

Round 1 - found 1 info

• ℹ️ README.md:151 - The return --force documentation still describes the flag only as skipping the dirty-check prompt, but the changed behavior now force-detaches and hard-resets/cleans worktrees so it can recover checked-out branches and conflicted states. Update the flag description to make the destructive cleanup behavior explicit, such as noting that it cleans/resets the worktree and returns it without prompting.

Round 2 (auto-fix) - found 1 info

• ℹ️ cmd/return_cmd.go:74 - The Cobra help text for treehouse return --force still says Skip dirty check prompt, but the changed behavior now force-cleans/resets and detaches the worktree before returning it. Update the flag description used by treehouse return --help so the built-in CLI documentation matches the README and the new destructive cleanup behavior.

Round 3 (auto-fix) - passed ✅

✅ **Lint** - passed

Round 1 - passed ✅

✅ **Push** - passed

Round 1 - passed ✅