Version manifest for upgrade tracking

[dean0x]

Problem

No version tracking for installed plugins. Users running devflow init can't tell if they're upgrading, reinstalling, or doing a fresh install. No mechanism to trigger data migrations when versions change.

Proposed Fix

Add .devflow/manifest.json with structure:

{
  "version": "1.0.0",
  "plugins": [
    { "name": "devflow-implement", "version": "1.1.0" }
  ],
  "installedAt": "2026-03-07T00:00:00Z",
  "updatedAt": "2026-03-07T00:00:00Z"
}

• Check on devflow init — compare installed vs package version
• Trigger migrations when version changes (e.g., path renames, setting schema updates)
• Display version info in devflow list

Scope

• Low-medium effort — new file, init-time check, migration framework