[#960] Price subscript notation for small USD values

[realproject7]

Summary

• Adds shared formatSubscriptPrice() utility in lib/format.ts that renders small decimals as $0.0₄6262 (subscript-zero notation, matching Mint Club style)
• Replaces toExponential() calls in PriceChart.tsx (formatUsdPrice and formatReservePrice) with subscript notation
• Updates formatUsdTokenPrice() in lib/usd-price.ts to use the same shared formatter

Fixes #960

Test plan

• Verify price chart Y-axis labels show subscript notation for small values
• Verify "Current price" text uses subscript notation
• Verify TokenPriceBox displays subscript notation for small USD prices
• Confirm no scientific notation appears anywhere in the UI

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[vercel]

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
plotlink	Ignored		Apr 23, 2026 10:11pm

[project7-interns]

Verdict: REQUEST CHANGES

Summary

The PR is close, but the new shared subscript formatter breaks for prices with 10 or more leading zeros after the decimal. In those cases it emits non-digit Unicode characters instead of valid subscript digits, so the display no longer matches the requested Mint Club-style format.

Findings

• [high] formatSubscriptPrice() only supports a single subscript digit. String.fromCharCode(0x2080 + leadingZeros) works for 0-9, but for 10+ leading zeros it produces unrelated characters (₊, ₋, ₓ, etc.). Example: 0.0000000000601 renders as $0.0₊6010 instead of a valid multi-digit subscript count. The repo already has a correct multi-digit mapping pattern in src/hooks/useTokenInfo.ts.
  • File: lib/format.ts:47
  • Suggestion: Convert leadingZeros to a string and map each digit to its subscript equivalent before joining, rather than deriving a single code point.

Decision

Requesting changes because this is a user-visible formatting bug in the new shared helper and would still violate the acceptance criteria for sufficiently small USD values.

[project7-interns]

Verdict: APPROVE

Summary

The re-review addresses the blocking formatter bug. Multi-digit leading-zero counts now render as proper digit-by-digit subscripts, so the shared helper matches the intended Mint Club-style format for very small USD values.

Findings

• No blocking findings.

Decision

Approving because the previous correctness issue in lib/format.ts is fixed and the change now satisfies the requested subscript-zero formatting behavior across the touched USD displays. CI checks were still pending at review time.