feat(onchain): migrate from StarkNet/Cairo to Stellar/Soroban (Rust)

[mercy60]

Migrates the entire chain stack from StarkNet + Cairo to Stellar + Soroban and rebrands the project from StellarHunt to StellarHunts.

Backend:

• Replace StarkNetHandlerService with StellarHandlerService (mock by default, real-mode serves as the seam for Soroban invokeHostFunction via @stellar/stellar-sdk).
• Update NFTClaimModule/service wiring and nft-claim unit tests.
• Update puzzle-category seed copy (StarkNet Deep Dive -> Soroban Deep Dive) and README env example (stellarshunt -> stellarshunts).
• Update rewards, user-report-card copy and example payloads.

Frontend:

• Wallet integration now targets Freighter / @stellar/freighter-api / @stellar/stellar-sdk (via NextAuth options + lib/data hints).
• Add shadcn Badge UI primitive; rewire homepage / referral / share components for Stellar branding.
• Drop package-lock.json from frontend in favour of the workspace root lockfile.

Onchain:

• Add Cargo workspace under onchain/contracts/ with four crates:
  • stellar-hunts (game logic, level progression, mint
    triggers, SHA256 answer hashing)
  • stellar-hunts-nft (per-level badge storage, role-gated
    minting keyed on env.invoker())
  • stellar-hunts-types (shared types as rlib)
  • stellar-hunts-receiver (test helper)
• All contracts target soroban-sdk 22.0.0 with a Soroban-flavoured
  release profile (opt-level z, lto, strip symbols, panic abort).

Toolchain & CI:

• Switch from Scarb / StarkNet Foundry to a Rust + Stellar CLI 22.x toolchain (.tool-versions, .github/workflows/build.yml).
• CI now runs cargo fmt --all -- --check, cargo build --workspace --release, and cargo test --workspace.

Docs:

• Rewrites top-level README, CONTRIBUTING, backend README, puzzle category README, rewards README, test-rewards.http, and docs/architecture.md for the StellarHunts / Soroban / Freighter stack.

Verified: ripgrep over the repo finds zero remaining references to StarkNet, Cairo, Scarb, snforge, ERC-1155, Argent, Braavos or openZeppelin.

Summary

Changes

Testing

Related Issues