Improve Taskbean PWA visual hierarchy

[nicholasdbrady]

Parent PRD: #47

Problem

The PWA makes filters, metrics, task cards, metadata, and actions feel similarly important. Users scanning for what needs attention must parse too many equivalent panels.

Scope

• app/public/index.html
• Dashboard shell, metric row, task columns/cards, metadata presentation, and visible task triage surfaces.

Acceptance criteria

• A clear primary focus region is visible in the default dashboard view.
• Metrics no longer compete visually with task cards.
• Secondary metadata such as timestamps/tags/agent labels is visually demoted without becoming unreadable.
• Existing compact Taskbean density and coffee-ledger identity are preserved.
• No new generic SaaS/card-grid visual language is introduced.

Required gates

• Playwright CLI snapshot/screenshot validates the default dashboard view.
• Impeccable live is used on the affected dashboard surface or a concrete limitation is documented.
• Code review reports no blocking findings.
• Rubber-duck analysis reports no blocking concerns.