Extend Strata19

There are four practical extension levels:

1. Skill: teach a supported workflow using existing public tools.
2. Routine: define a repeatable action graph with validation, approvals, and receipts.
3. MCP tool: add a new callable capability and declare every projection it needs.
4. Detector or interface contribution: change product source, catalogs, bundle output, tests, and release artifacts together.

Prefer the highest-level option that works. A skill is easier to review than a new tool; a routine is safer than a hand-built unattended loop; a detector should exist only when it has explicit evidence, limitations, and a declared execution surface.

Installed third-party detectors and arbitrary widget modules are not a public plug-in API today. Those changes are source contributions and must pass the repository's catalogs and release gates.