feat(9.75f-1): Implement FileBox dynamic plugin foundation

- Add workspace configuration to support plugins
- Create nyash-file plugin with C ABI
- Implement nyash_file_open/read/write/exists/free functions
- Add libloading dependency with dynamic-file feature
- Successfully build libnyash_file.so (1.55s build time)

Next: Implement plugin loader in interpreter

Cargo.toml

@@ -16,6 +16,8 @@ cli = []
 gui = ["dep:egui", "dep:eframe", "dep:egui_extras", "dep:image"]
 gui-examples = ["gui"]
 all-examples = ["gui-examples"]
+# 動的ライブラリサポート
+dynamic-file = ["dep:libloading"]
 
 [lib]
 name = "nyash_rust"
@@ -113,6 +115,9 @@ js-sys = "0.3"
 wabt = "0.10"
 wasmtime = "35.0.0"
 
+# 動的ライブラリロード（Phase 9.75f）
+libloading = { version = "0.8", optional = true }
+
 # GUI フレームワーク - only when gui feature is enabled
 egui = { version = "0.29", optional = true }
 eframe = { version = "0.29", default-features = false, features = ["default_fonts", "glow"], optional = true }
@@ -169,3 +174,11 @@ panic = "abort"
 # 開発用設定
 opt-level = 0
 debug = true
+
+# Workspace configuration
+[workspace]
+members = [
+    ".",                    # メインのnyash-rustプロジェクト
+    "plugins/nyash-file",   # FileBoxプラグイン
+]
+resolver = "2"