[DEPLOY-03] Configure Cloudflare R2

[kilip]

Description

Set up the Cloudflare R2 bucket for public media asset storage.

Subtasks

• DEPLOY-03-ST-01 Create R2 bucket
• DEPLOY-03-ST-02 Configure public access for media assets
• DEPLOY-03-ST-03 Set R2 credentials as environment variables
• DEPLOY-03-ST-04 Verify direct URL access (<img src>) works for uploaded assets

Acceptance Criteria

• DEPLOY-03-AC-01 Profile photos, org logos, and covers upload and serve correctly
• DEPLOY-03-AC-02 R2 bucket is publicly readable for media assets
• DEPLOY-03-AC-03 Upload size limits enforced (MAX_UPLOAD_SIZE)

Technical Notes

• Docs: TDD#2-tech-stack