feat: add interactive bounty flow diagram

[RYB-404]

Closes #851

Summary

• Adds an interactive React/SVG bounty lifecycle diagram for post -> claim -> work -> submit -> review -> payment
• Supports hover, focus, click, keyboard activation, animated stage transitions, and responsive stage selector controls
• Integrates the diagram into the How It Works page before the existing flow tabs
• Restores tracked frontend helper modules used by the existing app and updates .gitignore so frontend/src/lib is not ignored

Verification

• npm.cmd test -- bounty-flow-diagram.test.tsx
• npm.cmd run build

[RYB-404]

Solana/FNDRY payout wallet: 3Q4NGMeZftuULSmAB8ziqT2DYBfwzkqAYTng8SDrBnox