Fee and cost calculator widget

[truthixify]

Tier: M (2-4 days) | Type: feature

Context. The /use-cases page describes scenarios (payroll, DAO grants, refunds) but never puts a number on them. A calculator that estimates cost per stealth payment across supported chains at a chosen volume turns "sounds interesting" into "here is the annual cost." Adjacent to the Chain matrix (issue #7) but a distinct interactive tool.

Scope.

• Interactive widget: inputs = chain, payments per month, avg payment value; outputs = estimated network fee, stealth generation overhead, monthly total.
• Fee constants sourced from src/data/chains.json (see issue Dynamic Open Graph image generator #7); overhead constants documented in a comment block.
• Embeddable on /use-cases (below existing personas) and standalone on /use-cases/calculator.
• URL-encodes state so links to specific scenarios are shareable.

Acceptance.

• Calculator renders on both /use-cases and /use-cases/calculator
• Sharing a URL with query params reconstructs the same scenario
• Numbers cited on the page have inline source notes
• Keyboard-only operable
• Build passes
• Lighthouse Perf/SEO stay >= 90

Files. src/components/CostCalculator.tsx (new), src/pages/UseCases.tsx, src/App.tsx.

[cyber-excel10]

@cyber-excel10 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, i do like to work on this task . Can you please assign this to me .

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[ISTIFANUS-N]

@ISTIFANUS-N has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello there,
please permit this issue to work on

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