feat(cli): post-upgrade cleanup prompt + native mutation commands

[dipto0321]

Summary

After a successful upgrade, nodeup upgrade now asks whether to delete the old Node.js versions left behind. The prompt offers three options — y deletes every candidate, typing a specific version (e.g. 20.18.0) deletes only that one, and N (or empty enter) skips. Candidates are computed as installed \ {new LTS, new Current, currently active}.

To make the prompt actually reachable, this PR also fills in the Install, Uninstall, Use, SetDefault, GlobalNpmPrefix, and Current methods for all 7 working managers (fnm, nvm, Volta, asdf, mise, n, nodenv). The pre-existing stubs were returning ErrXxxNotImplemented, which made nodeup upgrade itself fail before even getting to migration or cleanup. Volta's and n's SetDefault remain intentional no-ops (those managers pin per-project, not per-machine). GlobalNpmPrefix returns the per-version npm global modules directory for each manager's on-disk layout. Current runs <manager> current (or per-manager equivalent) so we can exclude the active version from cleanup candidates.

nvm-windows stays unsupported and returns ErrNVMWindowsNotImplemented from Current; the prompt treats that error as "active version unknown" and proceeds without exclusion.

Pre-existing problem this PR also fixes

PR #20 merged end-to-end nodeup upgrade with m.Install(*v) and m.SetDefault(*latest) on lines 221/229 of internal/cli/upgrade.go, but every Manager implementation had those methods as stubs returning ErrXxxNotImplemented. This meant:

• nodeup upgrade would fail immediately at line 221 with ErrFNMNotImplemented (or whichever manager is active).
• Snapshot, migration, and the new cleanup prompt never executed.
• The stale TODO comments at fnm.go:155-169 said "will be filled in when the upgrade command (Phase 4) needs to mutate state", but Phase 4 was feat(cli): implement end-to-end upgrade command #20 itself.

Without implementing the mutation methods, the cleanup prompt is unreachable. So this PR expands scope: it ships the user-requested cleanup feature AND wires the mutations that make it actually work.

Manager interface change

New method on Manager:

Current() (semver.Version, error)

Used to detect the currently-active version so the cleanup prompt can exclude it. Returns ErrNVMWindowsNotImplemented for nvm-windows (honestly documenting the gap).

New CLI flags

• --cleanup — auto-confirm deletion of every candidate
• --cleanup-version <v> — only delete these versions (repeatable; pairs with --cleanup)

Existing --no-cleanup flag stays as the "skip everything" toggle. --yes implies --cleanup for non-interactive runs (e.g., CI).

Config equivalents

~/.nodeup/config.yaml:

cleanup:
  auto: false   # set true to skip the all-or-nothing prompt
  prompt: true  # set false to skip per-version confirm

Precedence (highest first): --no-cleanup > --cleanup (or cleanup.auto: true) > --cleanup-version <v> > cleanup.prompt: false > default interactive prompt.

Per-manager behavior

Manager	Install cmd	Uninstall cmd	Current query	Notes
fnm	fnm install <v>	fnm uninstall <v>	fnm current	Refuses to uninstall active
nvm	source nvm.sh && nvm install -s <v>	… nvm uninstall <v>	… nvm current	system / none → "unknown"
Volta	volta install node@<v>	volta uninstall node@<v>	First node@<v> row of volta list --format=plain	SetDefault is a no-op
asdf	asdf install nodejs <v>	asdf uninstall nodejs <v>	asdf current nodejs	Plugin name is nodejs
mise	mise install node@<v>	mise uninstall node@<v>	mise current node	Writes to ~/.config/mise/config.toml
n	n install <v>	n uninstall <v>	n current (n ≥ 8)	SetDefault is a no-op
nodenv	nodenv install <v>	nodenv uninstall <v>	nodenv version	Writes to ~/.nodenv/version
nvm-windows	unsupported	unsupported	returns ErrNVMWindowsNotImplemented	Documented limitation

Tests

• New internal/cli/cleanup_test.go — table-driven prompt tests covering: empty stdin (skip), y/n (delete-all vs skip), per-version y/n confirm, --cleanup (auto), --cleanup-version <v> (prefiltered), cleanup.auto config-driven, no candidates (skip with friendly note), exclusion logic (active version + new versions excluded), uninstall error handling (one failure doesn't block others).
• Updated internal/detector/<manager>_test.go for each of the 7 working managers + nvm-windows: replaced the "stub returns ErrXxxNotImplemented" tests with real ones that capture the shell-out argv and assert it matches the per-manager command shape.
• All tests pass with -race and 53.8% coverage.

Docs

• README.md — added a paragraph to Quickstart explaining the post-upgrade prompt.
• docs/managers.md — added a "Post-upgrade cleanup" section with the candidate-set formula, the flag table, the per-manager behavior table, and the failure modes.
• CHANGELOG.md — added entries under Unreleased → Added.

Closes

• feat(cleanup): post-upgrade cleanup prompt with version-by-version confirmation #41 (cleanup feature)

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[cocogitto-bot]

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