feat(runtime): Phase 103 CoreServices Optional化 - Memory Constraints対応

- Add CoreServicesConfig struct (from_env, minimal, all_enabled)
- Implement with_core_from_registry_optional() for selective initialization
- Update CoreBoxesImpl fields to Option<Arc<dyn XyzService>>
- Maintain backward compatibility (with_core_from_registry calls all_enabled)
- Add NYASH_CORE_DISABLE_* environment variable support
- ConsoleBox remains mandatory (Graceful Degradation principle)
- Add unit tests for optional initialization
- Update console_println! macro to handle Option type
- Fix direct console.println() calls in vm.rs and selfhost.rs
- Create core_optional_design.md documentation

Note: Phase 104 will extend ConsoleService to be optional as well with
graceful fallback in console_println! macro.

Files modified:
- src/runtime/plugin_host.rs (CoreServicesConfig, with_core_from_registry_optional, tests)
- src/runtime/core_services.rs (CoreBoxesImpl fields → Option type)
- src/runtime/mod.rs (console_println! macro updated)
- src/runner/modes/vm.rs (handle Option console)
- src/runner/selfhost.rs (handle Option console)
- docs/development/current/main/core_optional_design.md (new)
- docs/development/current/main/ring0-inventory.md (Phase 103 entry)

Test results:
- Build: ✅ Success (0 errors, 7 warnings)
- Unit tests: ✅ 3/3 passed (optional_core_tests)
- Runtime tests: ✅ 63/63 passed
- Smoke tests: ✅ 30/31 passed (1 pre-existing timeout)

src/runtime/core_services.rs

@@ -108,13 +108,17 @@ pub trait ConsoleService: Send + Sync {
 /// - Array → array
 /// - Map → map
 /// - Console → console
+///
+/// Phase 103: Optional化対応
+/// - 各サービスは Option<Arc<dyn XyzService>> に変更
+/// - ConsoleBox は必須（Graceful Degradation原則）
 pub struct CoreServices {
-    pub string: Arc<dyn StringService>,
-    pub integer: Arc<dyn IntegerService>,
-    pub bool: Arc<dyn BoolService>,
-    pub array: Arc<dyn ArrayService>,
-    pub map: Arc<dyn MapService>,
-    pub console: Arc<dyn ConsoleService>,
+    pub string: Option<Arc<dyn StringService>>,
+    pub integer: Option<Arc<dyn IntegerService>>,
+    pub bool: Option<Arc<dyn BoolService>>,
+    pub array: Option<Arc<dyn ArrayService>>,
+    pub map: Option<Arc<dyn MapService>>,
+    pub console: Option<Arc<dyn ConsoleService>>,
 }
 
 impl std::fmt::Debug for CoreServices {