feat: add company management and resume book sponsor editing ✨

[NyranMoodie]

Description ✏️

Adds admin tooling to manage companies and resume book sponsorships.

• Add Companies admin page with create, edit, and delete flows
• Support creating companies from LinkedIn (Apify) with a manual fallback when Apify is unavailable
• Allow editing resume book sponsors after creation
• Allow deleting resume books that have zero submissions
• Extract shared ResumeBookSponsorsField for create/edit modals
• Document APIFY_API_TOKEN in admin dashboard .env.example

Type of Change 🐞

• Feature - A non-breaking change which adds functionality.
• Fix - A non-breaking change which fixes an issue.
• Refactor - A change that neither fixes a bug nor adds a feature.
• Documentation - A change only to in-code or markdown documentation.
• Tests - A change that adds missing unit/integration tests.
• Chore - A change that is likely none of the above.

Checklist ✅

• I have done a self-review of my code.
• I have manually tested my code (if applicable).
• I have added/updated any relevant documentation (if applicable).

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