feat: add org profile landing page

[HeyItsGilbert]

Stack position: 7 of 7 — merge last

The org landing page shown at github.com/PowerShellOrg.

What's in this PR

profile/README.md:

• One-sentence org description
• Tool roster table: Plaster and PSDepend with status badges (status-active)
• "Want us to adopt your tool?" CTA → links directly to the tool_adoption_request.yml template
• "Want to help?" CTA → links to good-first-issues and help-wanted label searches across the org
• Links to GOVERNANCE.md and CODE_OF_CONDUCT.md

Council questions

1. Org description: "PowerShellOrg is a community-run GitHub organization that adopts and maintains open-source PowerShell tools that would otherwise go unmaintained." — Does this capture what we are?
2. Tool roster: Plaster and PSDepend are the two initial entries. Should Plaster's status badge be active or stable? It's been maintained longer.
3. Status badge style: currently using shields.io static badges. Would you prefer something dynamic (e.g., pulling from actual CI status)?
4. Anything missing from the landing page that a first-time visitor would want to see?

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Base: pr/06-docs — merge PRs 1–6 first. This is the last PR in the stack.