feat(runtime): modularize host capabilities

- add an exact-version Capability Registry and structured descriptors
- move Clock bindings, host state, and Linker installation into its own module
- derive required capabilities from Component imports and link only requested interfaces
- cover exact-version resolution and minimal per-component capability sets

crates/wasmeld-runtime/src/lib.rs

@@ -6,10 +6,12 @@
 //! service exports, and invokes it through one serial Actor.
 
 mod bindings;
+mod capability;
 mod error;
 mod manifest;
 mod runtime;
 
+pub use capability::CapabilityDescriptor;
 pub use error::RuntimeError;
 pub use manifest::{ResourceLimits, ServiceKey, ServiceManifest};
 pub use runtime::{ActorHandle, Runtime, RuntimeConfig, RuntimeStats};