Implement clinic branding and presentation polish for final demo environment

[inteee]

Description

Hackathon judging benefits from a more deliberate product presentation without derailing engineering work.

Scope

• Add configurable clinic name/logo placement
• Tighten visual hierarchy on landing, login, dashboard, and billing
• Keep styles consistent with shared design tokens
• Avoid major functional rewrites

Acceptance Criteria

• Key screens look productized and coherent
• Branding can be changed without code churn
• UX polish does not break existing workflows

Dependencies

Blocked by #227

Stack

Next.js / React Native