perf(plugin-native): move runtime_param_schema and get_source_config to worker thread

[staging-devin-ai-integration]

Context

runtime_param_schema (wrapper.rs:776) and get_source_config (wrapper.rs:1250) remain synchronous/unguarded outliers — they are called on the async side without timeout, catch_unwind, or routing through the worker thread.

What needs to happen

1. Route both calls through the worker thread's WorkerRequest channel (add new variants)
2. Apply the same catch_unwind + timeout pattern used for other FFI calls
3. Handle the chicken-and-egg problem: get_source_config is called before the tick loop starts, and runtime_param_schema is called during node registration (before the worker exists)

Why not now

This was identified during the PR 3 (worker thread) review. Both calls happen at low frequency (once per instance creation / start), so the risk is low. The refactor requires rethinking the call timing vs. worker lifecycle, which is better handled as a separate change.

References

• TODOs at wrapper.rs:776 and wrapper.rs:1250
• PR 3 review thread (nit Playwright E2E tests #10)