docs: mark P1.1 asset provider interface tasks complete

feat(assets): add AssetManager with sync/async fetch and ref tracking

feat(assets): add ByTag and ByRole query methods to manifest

feat(assets): add AssetManifest with load/save and assessment types

feat(assets): add AssetFormat enum with String()

feat(assets): add AssetHandle with atomic ref counting

feat(assets): add AssetProvider interface and AssetResult

docs: add P1.1 asset provider implementation plan

docs: add P1.1 asset provider interface design

Refactor combat resolver and related structures for clarity and consistency

docs: add mandatory unit test policy to CONVENTIONS.md

feat: GoForge Phase 0 — engine foundation