docs(wit): sketch Numax host API

[lntutor]

Summary

• add three independent, parseable WIT packages for database, logging, and GCounter capabilities
• keep the definitions explicitly exploratory with no runtime or SDK wiring
• document current status, validation, and open migration, world, error, value, and versioning questions

Verification

• wasm-tools component wit wit/numax-db.wit
• wasm-tools component wit wit/numax-log.wit
• wasm-tools component wit wit/numax-crdt.wit
• cargo test --workspace -q (498 passed)
• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• git diff --check

Closes #61

[lntutor]

Current head ccdbbf9566e9ff33af9239ca265d1b8a62e38781 is mergeable and the visible CI surface on this exact SHA is fully green: cross-platform Check, Clippy, and Test jobs on Ubuntu, macOS, and Windows; Format; Build WASM Examples; CLI Multi-process Smoke; Benchmark Comparator Tests; Ubuntu Profiling Artifacts; Benchmark Regression Gate; and the aggregate CI Success check all completed successfully. There are no review threads or review-body comments open on the current PR state, so if this Numax host API documentation still matches the intended direction, it looks ready for maintainer review/merge when convenient.