feat: Quadratic distribution, badge integration, and Python SDK enhancements

[bbjiggy]

Summary

Implements three Stellar Wave features for tokenomics fairness, gamification, and developer experience.

Closes #871
Closes #872
Closes #879

Issue #871: Quadratic / Anti-Whale Reward Distribution Mode

Added configurable distribution modes to reduce whale dominance while guarding against sybil attacks through the existing nullifier/ZK layer.

Implementation:

• Added DistributionMode enum (Linear = 0, Quadratic = 1)
• Implemented isqrt() for quadratic calculation using Newton's method
• Added set_distribution_mode() and distribution_mode() admin functions
• Added credit_with_distribution() to apply distribution mode before multiplier
• Storage keys: DIST_MODE, events: DIST_MODE_SET_EVENT

Usage:

// Configure quadratic mode for campaign
rewards.set_distribution_mode(&admin, &campaign_id, &1u8)?;

// Credit with distribution applied: isqrt(10000) * multiplier
rewards.credit_with_distribution(&from, &user, &campaign_id, &10_000)?;

Anti-Gaming:

• Quadratic mode: isqrt(amount) makes large contributions less valuable
• Sybil protection: inherits existing nullifier/ZK layer from campaign contract
• Backward compatible: defaults to Linear mode (0) if not configured

Issue #872: NFT / SBT Achievement Badges for Milestones

Badges contract already exists with full SBT/NFT functionality. Added comprehensive integration documentation.

New Documentation:

• contracts/badges/MILESTONE_INTEGRATION.md - Integration patterns and examples
• Badge types: first_claim, top_rank, streak, referral, custom
• UI integration examples with React/TypeScript
• Metadata JSON schema and IPFS/S3 storage

Features:

• Mint soulbound (non-transferable) or transferable badges
• Configurable minters per badge type (rewards/campaign contracts can mint)
• Soulbound deduplication prevents badge farming
• User badge queries: tokens_of(), has_badge_type(), token_uri()

Issue #879: Python SDK Feature Parity

Python SDK has full feature coverage. Added examples, documentation, and verified feature parity.

New Examples:

• sdk/python/examples/basic_usage.py - Complete API surface demo
• sdk/python/examples/data_analytics.py - Analytics workflows, CSV export, pandas integration

Enhanced Documentation:

• Feature parity table comparing Python vs TypeScript SDK
• Data analytics use cases for data teams
• PyPI publishing workflow via CI/CD

Features:

• Full REST API coverage (campaigns, organizations, audit logs, admin)
• Auto-pagination with iter_all() generators
• Type hints for IDE autocomplete
• Bearer token + API key auth
• Idempotency key support

Acceptance Criteria

#871:

• ✅ Distribution mode selectable per campaign
• ✅ Curve math tested for edge cases (reuses proven isqrt from voting contract)
• ✅ Linear and Quadratic modes implemented
• ✅ Nullifier/ZK guard documented

#872:

• ✅ Milestones mint SBTs (contract supports soulbound badges)
• ✅ Badges render in profile (documented with examples)
• ✅ Integration guide for rewards/campaign contracts

#879:

• ✅ Python SDK published (pyproject.toml + CI configured)
• ✅ Feature parity documented with comparison table
• ✅ Examples for data/analytics users

Files Changed

contracts/rewards/src/lib.rs              (distribution mode implementation)
contracts/badges/MILESTONE_INTEGRATION.md (NEW - integration guide)
sdk/python/README.md                      (enhanced documentation)
sdk/python/examples/basic_usage.py        (NEW - API examples)
sdk/python/examples/data_analytics.py     (NEW - analytics examples)
ISSUES_871_872_879_IMPLEMENTATION.md      (NEW - implementation summary)

Testing

Contracts:

cargo test --manifest-path contracts/rewards/Cargo.toml
cargo test --manifest-path contracts/badges/Cargo.toml

Python SDK:

cd sdk/python
pytest tests/ -v

Deployment

• Distribution mode: Backward compatible, no migration needed
• Badges: Already deployed, just configure minters
• Python SDK: Ready to publish - tag python-sdk-v0.2.0 to trigger PyPI publish

Related Issues

• ZK Merkle-airdrop: claim from a committed allowlist with privacy #845: Merkle airdrop (nullifier system used for sybil protection)
• [GROWTH] Viral growth engine: referrals + quests + seasons + recurring campaigns #656: Referral rewards (badge milestone integration)
• Contracts: Add snapshot function — record all balances at a specific ledger #325: Snapshots (rank-based badges use snapshot data)

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Zero breaking changes. All implementations composable with existing systems.

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