feat: include directory targets in update and uninstall via recorded ownership #342

Phase A work unit 2 of the maintainer-approved scoped plan (docs/design/issue-332-powershell-windows.md, Phase A revision v2). Depends on the install directory target (work unit 1).

Scope

• cortex update refreshes capabilities in a previously installed directory target using the recorded manifest and ownership.
• Conservative uninstall removes exactly the files Cortex owns in the directory target and nothing else; user-owned files in the same directory are untouched.
• Backups and rollback behave as for the existing runtimes.

Acceptance criteria

• Update after upstream content changes rewrites only affected owned files, with readback and manifest refresh.
• Uninstall removes only owned files; a directory containing foreign files keeps them and reports what was left.
• Running update/uninstall against a directory with no prior Cortex ownership fails closed with an explicit diagnostic.

Checks

• Install/update parity harness extended to directory targets; uninstall ownership isolation test (owned vs foreign files).

Refs #332