docs: update GitHub Pages documentation with v0.3.0 typing

Updated all GitHub Pages docs to reflect 99% type coverage.

**Changes:**
- Updated docs/index.md with v0.3.0 features and 99% coverage
- Created docs/guide/type-coverage.md - comprehensive typing guide
- Updated docs/guide/fully-typed-usage.md with v0.3.0 note
- Removed docs/api/typed-client.md (obsolete - typing now in main client)

**New Documentation:**
- Type coverage statistics and breakdown
- Response type patterns (4 types)
- Field mixins explanation
- Migration guide from v0.2.x
- Benefits of full typing
- Complete examples

GitHub Pages will show updated docs on next deployment.

Author: BenjaminWatts