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/leak_tracker.rs

@@ -1,6 +1,7 @@
 use once_cell::sync::Lazy;
 use std::collections::HashMap;
 use std::sync::Mutex;
+use crate::runtime::get_global_ring0;
 
 static ENABLED: Lazy<bool> =
     Lazy::new(|| std::env::var("NYASH_LEAK_LOG").unwrap_or_default() == "1");
@@ -41,12 +42,14 @@ impl Drop for Reporter {
         if m.is_empty() {
             return;
         }
-        eprintln!("[leak] Detected {} non-finalized plugin boxes:", m.len());
+        get_global_ring0()
+            .log
+            .warn(&format!("[leak] Detected {} non-finalized plugin boxes:", m.len()));
         for ((ty, id), _) in m.iter() {
-            eprintln!(
+            get_global_ring0().log.warn(&format!(
                 "  - {}(id={}) not finalized (missing fini or scope)",
                 ty, id
-            );
+            ));
         }
     }
 }