Epic: Add organization creation onboarding flow

[wauputr4]

Context

User feedback from Multica PEN-82: current product appears to only support claiming existing organizations. If there is no clear create organization option in console/account, add a dedicated organization onboarding/create page and plan it for follow-up work.

Current repo notes from quick triage:

• Public/account copy is claim-first: users are directed to find an existing organization and submit a claim.
• /console delegates to the admin workspace and there is an existing create organization action in the admin/console implementation.
• There is not yet an obvious user-facing onboarding route/flow for "my organization is not listed, create it".
• Existing related GitHub issues: Pre-release: Complete admin organization create/edit fields audit #42 admin organization create/edit fields audit, Pre-release: Harden auth and organization claim API behavior #41 auth/claim API hardening.

Goal

Add a clear, safe organization creation onboarding path for users whose organization is not listed yet, while preserving the claim flow for organizations that already exist.

Child issues

• Define organization creation onboarding UX and entry points #78 Define organization creation onboarding UX and entry points
• Implement create organization onboarding page in console/account #79 Implement create organization onboarding page in console/account
• Harden organization creation API contract and permissions #80 Harden organization creation API contract and permissions

Definition of done

• Users can clearly choose between claiming an existing organization and creating/onboarding a new organization.
• Dedicated create/onboarding route and entry points exist from relevant empty/search/account/console states.
• Backend permission, validation, duplicate, and ownership semantics are tested and documented.
• Frontend mobile/dark-mode usability is covered in the implementation review.
• Relevant frontend/backend checks pass, or skipped checks are documented in the implementation PR.