Organization profile and default community health files for Oxidean.

• profile/README.md — rendered on the Oxidean org page
• profile/oxidean-mark.png — brand mark used by the profile (vector and usage notes live in oxidean/oxidean → brand/)
• CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, SUPPORT.md, PULL_REQUEST_TEMPLATE.md, ISSUE_TEMPLATE/ — defaults that apply to every repo in the org that doesn't define its own

Product links: Oxidean Cloud at app.oxidean.dev, marketing site at oxidean.dev.