fix(cli): thread cmd.Context() through packages snapshot/restore

[dipto0321]

Summary

internal/cli/packages.go's runSnapshot and runRestore are cobra RunE functions with a live cmd.Context() available, but both called context.Background() directly. Ctrl-C during nodeup packages snapshot or nodeup packages restore could not cancel the in-flight npm ls -g / npm install -g subprocess — the child process kept running after the user aborted.

This is the same contextcheck violation internal/cli/upgrade.go and check.go already addressed as part of #48 (the manifest fetch fix). packages.go was the last RunE file in the tree still using context.Background(). Fix: replace both call sites with cmd.Context(), drop the now-unused "context" import.

Closes #49.

Linked issues

• Closes fix(cli): context.Background() used instead of cmd.Context() in packages.go (contextcheck violation) #49

Type of change

• fix — bug fix (PATCH bump)

Checklist

• Title follows Conventional Commits (fix(scope): subject)
• I ran make ci locally and it passes (fmt, vet, test pass locally; make lint fails on the v2→v1 schema mismatch tracked in build(lint): .golangci.yml v1 schema incompatible with golangci-lint v2 (brew installs v2, make lint fails to even parse config) #62 — pre-existing on main, independent of this fix; CI runs golangci-lint v1.64.8 per .github/workflows/ci.yml and parses the config fine)
• I added or updated tests for the change (N/A — three-line behavioral fix; the contract is already covered by the cobra cmd.Context() integration with contextcheck. A focused test would require mocking packages.Snapshot/packages.Restore, which is a larger refactor than this fix wants. The pre-existing internal/packages/snapshot_test.go::TestSnapshot_StoredVersionKeyMatchesArg and TestRestoreFromSnapshot_ReadsSourcePathRegardlessOfNodeVersion cover the contract pieces the cli calls.)
• I updated relevant docs (README, docs/, inline godoc)
• No new linter warnings (this PR actually REMOVES a contextcheck violation that was previously suppressed in the local make lint output but not in CI — once build(lint): .golangci.yml v1 schema incompatible with golangci-lint v2 (brew installs v2, make lint fails to even parse config) #62 is fixed, this would have been the only remaining offender)
• If breaking: I documented the migration path in the PR body and updated CHANGELOG.md (N/A — no CLI surface breaking)

Scope notes

• runSnapshot was a single-line change: packages.Snapshot(context.Background(), m.Name(), version) → packages.Snapshot(cmd.Context(), m.Name(), version).
• runRestore was a two-line change: ctx := context.Background() → ctx := cmd.Context(); the rest of the function already used the local ctx, so only the source needed updating.
• The "context" import is now unused and was removed.
• I did NOT thread cmd.Context() through getCurrentVersion (the helper at line 63) because it doesn't shell out — it just calls m.ListInstalled(), which is an in-memory slice operation. There's no Ctrl-C behavior to expose there.
• I deliberately did NOT refactor runRestore to be unit-testable with a cmd.Context() injection seam. Same reasoning as bug(packages): restore aborts on first failed install; migration report never written #46: a stubbed platform.RunShell seam is a larger change than this three-liner wants, and the rest of the test surface (snapshot_test.go + restore_test.go) already validates the package-level Snapshot/Restore contract that runRestore relies on.

Out of scope (separate issues)

• --cleanup / --yes precedence conflict — bug(cli): --yes silently overrides --no-cleanup, auto-deletes with zero confirmation #57.
• Path traversal in packages restore/diff via unsanitized manager name — fix(packages): path traversal via unsanitized manager name in packages restore/diff #51.
• asdf ASDF_DIR vs ASDF_DATA_DIR inconsistency — fix(detector): asdf uses ASDF_DIR vs ASDF_DATA_DIR inconsistently between docs, detector, and system-node classifier #50.
• Current() failure leaves active Node unprotected from cleanup — bug(cli): Current() failure leaves the active Node version unprotected from cleanup deletion #58.
• n manager's Current() relies on unverified n current subcommand — fix(detector): n manager's Current() relies on unverified 'n current' subcommand #59.

Screenshots / output

User-visible behavior change:

• Before: User runs nodeup packages snapshot, hits Ctrl-C during the in-flight npm ls -g step. The cobra command returns immediately but the underlying npm child process keeps running until completion (or its own timeout). The new cmd.Context() plumbing makes Ctrl-C now propagate down through RunShell to exec.CommandContext, killing the child.
• After: Ctrl-C during nodeup packages snapshot or nodeup packages restore cancels both the cobra command AND the in-flight npm subprocess.

Verification path: start nodeup packages snapshot, watch the in-flight npm PID via ps, send SIGINT to the parent nodeup process, confirm the child npm PID disappears within ~ms.

[cocogitto-bot]

✔️ 564fc90 - Conventional commits check succeeded.