Bring GitHub org/user discovery into Create-Project wizard

[adoLime]

User Story

As an Admin, I want to pick GitHub repositories from an organization/user while creating a project, so that I don't have to know each repo's exact owner/name in advance.

In Scope

• Add an org/user discovery picker to ProjectSourcesStep (Create-Project wizard, Step 2), reusing the existing discoverRepositories service.
• Browse flow: enter org/user + token → paginated repo list → multi-select repos to stage for the new project.
• Keep the manual owner/name entry as a fallback (as already supported by AddSourceModal via its githubMode toggle).
• Deduplicate against already-staged repos in the wizard (same owner/name guard already exists for manual entries).
• Reuse the discovery UI patterns from AddSourceModal where sensible; extract shared pieces if it reduces duplication.

Acceptance Criteria

• In the Create-Project wizard, Step 2, the admin can switch between "Discover from org/user" and "Enter owner/name directly".
• Discovery: enter an org or user + token → a paginated, searchable list of repositories is shown.
• The admin can select multiple repos from the discovery list and add them to the wizard's draft sources in one action.
• Selected discovered repos flow through the existing onAdd → connectDraftSources path, exactly like manually-entered repos.
• Partial-failure handling (project created, some repos fail to connect) works the same way as for manually-added sources (retry per source).
• Empty / loading / error / rate-limit states for discovery are handled (consistent with AddSourceModal).
• Works in light and dark themes; keyboard focus stays visible; accessible labels.
• Unit tests cover the new discovery branch in the wizard context.