feat(sdk): add C++ implementation files for all services
Complete C++ SDK with implementation stubs for:
- Database (KV, Document, Vector, TimeSeries stores)
- Hosting (domains, DNS, deployments, SSL)
- Bridge (cross-chain transfers, relayers)
- Mining (pool connection, device management)
- Economics (pricing, billing, staking)
- Governance (proposals, voting, DAO, vesting)
- Privacy (confidential tx, ring signatures, stealth addresses)
- Contract (deployment, interaction, events, multicall)
All 12 languages now have complete 12-service SDK coverage.
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