feat(plugins): add portable plugin lockfile

[artrixdotdev]

Description

Adds a portable ~/.config/DankMaterialShell/plugins.lock.json that stays synchronized with managed plugin installs, updates, and removals.

• Records each plugin repository, optional monorepo path, and exact Git commit
• Adds dms plugins lock and dms plugins restore [lockfile], with optional --prune
• Migrates existing managed installs, preserves shared monorepo revisions, and validates/atomically writes lockfiles

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behavior)
• Refactor / internal cleanup
• Documentation
• Other

Related issues

None.

Screenshots / video

Not applicable; this is a CLI and backend change.

Checklist

• My code follows the conventions in CONTRIBUTING.md
• I have tested my changes locally
• New user-facing strings are wrapped in I18n.tr() with translator context, reusing existing terms where possible (no QML strings added)
• Go changes: ran make fmt, added/updated tests, make test passes, and go mod tidy is clean
• QML changes: not applicable
• I have opened a corresponding pull request in dlx-docs to document the new behavior: docs(plugins): document lockfile restore workflow DankLinux-Docs#122