Task 3.2: Update GitHub App listing description and screenshots

[ajianaz]

Task: GitHub App Listing Update

Update the apps/code-cora listing to reflect V2 Open Core positioning.

Updates

• Description: "Cora — Open Source AI Code Review. BYOK. MIT License."
• Website URL: https://codecora.dev
• Remove SaaS pricing references
• Update screenshots: V2 website + CLI output (replace V1 TypeScript screenshots)
• Verify listing at https://github.com/apps/code-cora

Screenshot Content Ideas

• CLI output showing review findings
• PR comment with cora review
• Website hero section
• 4-platform install section

Part Of: #118, #121
Depends On: #130 (website deployed), #132 (backend MVP)