docs: add Privacy Policy link and support contact required for Kiro powers registry submission

Context

Kiro's powers registry is curated: you apply at kiro.dev/powers/submit and they reach out if it's a fit. There is no self-service publish and no PR-a-manifest route — kirodotdev/powers is only a subset of the catalog, and its CONTRIBUTING.md redirects submissions to that form.

Getting listed puts dataiku-headless in the Available section of Kiro's Powers panel, i.e. discoverable without anyone pasting a GitHub URL.

What's missing

Kiro's stated requirements are met by plugin.json already ($schema, name, version, description, author name + URL, activation keywords, SPDX license). Two README requirements are not:

• Privacy Policy link. Nothing in the repo, and nothing in git history (git log -S'privacy' -- '*.md' is empty across all branches). Needs a decision on whether to point at Dataiku's corporate policy or write a short page scoped to this tool.
• Support contact. No SECURITY.md, no CONTRIBUTING.md; .github/ has only workflows. Needs a decision: GitHub issues, or a Dataiku support channel.

Worth stating plainly in whatever the privacy section says: the server holds a Dataiku URL and a personal API key in ~/.dataiku/config.json (0600), sends them only to the configured instance, and the repo ships no telemetry. A reviewer assessing a power that handles customer credentials will look for exactly that.

Blocked on

The submission form requires a public repo URL containing plugin.json. That file does not exist on main — it arrives with #91, and #67 builds on it.

• #91 — ships the portable Agent Plugins package (root plugin.json + mcp.json)
• #67 — Kiro power install docs, displayName, keyword narrowing

Both need to land on main before the form can be filled in.

Done when

README has both sections, and the submission form has been sent.

Read the README requirements in this issue, then inspect the changes from #91 and #67, especially root plugin.json and the Kiro install documentation. Resolve the privacy-policy and support-contact choices before documenting them, and wait until both dependencies are on main. Done means the README has both sections and the Kiro submission form has been sent.