Close remaining uninstall host-integration recovery gaps

[backnotprop]

Context

Non-blocking follow-up from the independent review of #1177. The PR is merge-ready, but two pre-existing host-cleanup gaps remain.

Problems

1. Missing host CLI guidance assumes the host will return. When a detected integration cannot be removed because its CLI is unavailable, the message only tells the user to restore that CLI on PATH. If the host was permanently uninstalled, the actionable recovery is to remove the exact Plannotator entry from the host configuration and rerun uninstall. Verified example: remove the Plannotator entry from enabledPlugins in ~/.factory/settings.json.

2. Customized Plannotator hooks can survive binary removal. Managed-hook detection currently matches exact command strings. A hook using a documented option, such as plannotator --browser Safari, is not recognized and can be left pointing at a deleted binary.

Required behavior

• For an unavailable host CLI, report both recovery routes: restore the CLI and rerun, or remove the exact detected Plannotator configuration entry and rerun. Name the file and field.
• Recognize Plannotator hook commands that include supported arguments without claiming unrelated custom commands.
• Before binary removal, detect remaining recognized host references to the Plannotator binary/command. If any remain, fail closed with the exact file, field, and cleanup guidance.
• Preserve unrelated user hooks and configuration in the same file.
• Keep the normal-uninstall versus purge data contract unchanged.

Regression coverage

• Missing/permanently removed Droid CLI with a Plannotator enabledPlugins entry.
• Customized managed hook such as plannotator --browser Safari.
• A user-owned hook beside the managed hook survives cleanup.
• Binary removal remains blocked while a recognized Plannotator reference survives, then succeeds after manual cleanup.

Evidence

Independent review of #1177 reproduced both behaviors against a compiled binary. Neither blocks #1177.