refactor(host): bind capabilities and async execution

[fffonion]

Summary

• Binds capability profiles to host imports and builtins.
• Adds generic async host drivers and host-owned policy/state boundaries.
• Finalizes async IO ownership and absorbs the implementation from feat(host): submit async functions through generic drivers #19 and the non-HTTP portions of refactor(host): isolate host-owned policies and async IO #20.

Stack

• Base: refactor(vm): unify host runtime lifecycle #16
• Next: feat(vm): expose cancellable invocation item streams #23

Verification

• Proc macro, capability, async host, async IO, runtime host, and SQLite focused suites passed
• Strict Clippy passed

Supersedes

• feat(host): submit async functions through generic drivers #19
• Non-HTTP portions of refactor(host): isolate host-owned policies and async IO #20