Add USD values across all dashboards — Writer, Reader, Portfolio

[realproject7]

Problem

Writer Dashboard, Reader Dashboard, and Portfolio all show PLOT values without USD equivalents. Users need dollar context to understand their earnings and holdings.

Requirements

1. Writer Dashboard (src/app/dashboard/writer/page.tsx)

Add USD next to:

• TOKEN PRICE: 0.0030 PLOT (≈ $0.05)
• TVL: 492.21 PLOT (≈ $8.09)
• ROYALTIES: 3.937 PLOT (≈ $0.06)

2. Reader Dashboard — Portfolio (src/components/ReaderPortfolio.tsx)

Add USD next to:

• TOTAL VALUE: 830.51 PLOT (≈ $13.66)
• Per-holding value: 830.51 PLOT (≈ $13.66)

3. Reader Dashboard — Trading History (src/app/dashboard/reader/page.tsx)

Add USD next to:

• Trade amounts: 83.81 PLOT (≈ $1.38)

Display format

Muted text, smaller font: (≈ $X.XX)

Use the existing PLOT→USD price from lib/usd-price.ts. Fetch once and pass through — don't make separate price calls per component.

Files to modify

• src/app/dashboard/writer/page.tsx — token price, TVL, royalties
• src/components/ReaderPortfolio.tsx — total value, per-holding value
• src/app/dashboard/reader/page.tsx — trade amounts

Branch

task/672-dashboard-usd-values

Self-Verification (T3)

• Writer Dashboard: USD shown for token price, TVL, royalties
• Reader Portfolio: USD shown for total value and per-holding
• Reader Trading History: USD shown for trade amounts
• USD values use existing PLOT price source (no new API calls per row)
• Mobile responsive — doesn't overflow
• npm run build passes