test: add unit tests for createRuntimeDependencies default wiring (Issue #114)

[rafaio1]

Summary

Adds unit tests verifying createRuntimeDependencies correctly wires all nine dependency keys with proper defaults and respects injected overrides.

Tests Added

• ✅ All required dependency keys present with non-null instances
• ✅ Default implementations verified (InMemoryMemoryStore, UnconfiguredModelProvider, ConsoleRuntimeLogger, InMemoryRuntimeStateStore, RuntimeEventBus)
• ✅ Injected memoryStore and eventBus respected over defaults

Verification

All 8 tests pass locally via npx vitest run tests/runtime/create-runtime-deps.test.ts.

Closes #114