refactor(host): explicit host for configuration reads and one entered runtime store #3794

Part of #3747. Follow-up to #3763 and #3772, which leave two pieces deferred in their PR bodies.

1. Narrow commandHostEnvironment() to command execution

About 60 call sites remain in the root platform-runtime-* files and the platform packages. They read configuration (toolchain and SDK paths, caches, path resolution) through the ambient, AsyncLocalStorage-bound commandHostEnvironment(). The holistic review on the stack decided:

• Configuration reads take the host explicitly. Pass it as a parameter, through the runtime deps, or through a port bound at construction.
• The ambient lookup is only for host-kit command execution and diagnostics.

Done when:

• Every non-test call of commandHostEnvironment() outside host-kit's command execution and diagnostics is replaced by an explicit host.
• A test on the daemon route proves configuration is read from the runtime's host and not from the process, when the two differ.

2. One entered runtime store

#3772 moved per-runtime state onto defineRuntimeSlots. Each module still exposes its own handle, collected into runtimeStates.

Required:

• Collapse them into one store, entered once per runtime.
• Modules declare slots; the runtime owns entry and disposal.

Done when:

• No module-level handle or runtimeStates aggregation remains.
• The two-runtime isolation tests (Apple runner, Android helper, PNG worker, daemon modules) still pass.

Ordering

• feat(host): startAgentDevice() for embedder-owned daemons #3757 (agent-device/host) does not depend on this issue.
• chore(layering): forbid process globals outside entry points #3753 (lint gate) should land after part 1, so the gate can also forbid commandHostEnvironment() outside the command-execution boundary.