v0.5.0

The plugin is renamed: opencode2-cow-worktree is now opencode-cow-worktree.

• The package name, plugin id, and TUI id carry the new name. Install with
  opencode2 plugin add opencode-cow-worktree, or
  "package": "opencode-cow-worktree@latest" in opencode.json. The GitHub
  repository moved to rbelem/opencode-cow-worktree; GitHub redirects old
  links.
• CoW capability probes write scratch directories prefixed
  .opencode-cow-capability- (was .opencode2-cow-capability-). Leftover
  scratch from older versions is inert: cleanup is in-process and nothing
  scans for the old prefix.
• The dogfood install check now matches the 20260917 nightly's API: readiness
  polls GET /api/plugin (/api/health lost its handler on the 20260915
  nightly), activation is detected by polling the plugin list, and worktree
  endpoints carry projectID.
• Suite: 348 tests; the dogfood install check passes 12/12 against the
  20260917 nightly.