v0.3.0

Added

• lean-semantic-search-runtime: a package-owned runtime crate that ships the LeanSemanticSearch Lean capability
  payload, materializes it in a caller-owned per-toolchain cache with a generated downstream lean-toolchain, records
  provenance, builds via CargoLeanCapability::lean_sysroot, and returns a LeanBuiltCapability for downstream hosts.

Changed

• lean-semantic-search-runtime now delegates source-package materialization to the shared lean-toolchain helper
  while preserving its public runtime API. Cache keys remain digest/toolchain based, provenance sidecars and generated
  downstream lean-toolchain files are still recorded, and the runtime payload remains a zero-dependency Lake package.