extract shared mosis-core library from sandbox APIs

Create core/ directory with platform-agnostic sandbox components:
- Timer manager, JSON API, Crypto API, Virtual FS
- Lua sandbox, Permission gate, Audit log, Rate limiter
- Platform abstraction interfaces (IAssetInterface, IFilesystemInterface)
- Platform-agnostic logger with Android/Desktop implementations

Update designer to link against mosis-core library instead of
including sandbox sources directly.

This is the foundation for unifying the Android service and
desktop designer to share the same codebase.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

core/include/mosis/platform/asset_interface.h

@@ -0,0 +1,57 @@
+#pragma once
+
+#include <string>
+#include <vector>
+#include <memory>
+
+namespace mosis {
+
+/**
+ * Platform-agnostic interface for loading assets.
+ * Android implements this using AAssetManager.
+ * Desktop implements this using filesystem operations.
+ */
+class IAssetInterface {
+public:
+    virtual ~IAssetInterface() = default;
+
+    /**
+     * Read entire file contents as bytes.
+     * @param path Relative path to asset (e.g., "apps/home/home.rml")
+     * @return File contents, or empty vector if not found
+     */
+    virtual std::vector<uint8_t> ReadFile(const std::string& path) = 0;
+
+    /**
+     * Read entire file contents as string.
+     * @param path Relative path to asset
+     * @return File contents, or empty string if not found
+     */
+    virtual std::string ReadFileString(const std::string& path) = 0;
+
+    /**
+     * Check if an asset exists.
+     * @param path Relative path to asset
+     * @return true if asset exists
+     */
+    virtual bool Exists(const std::string& path) = 0;
+
+    /**
+     * List files in a directory.
+     * @param path Relative path to directory
+     * @return List of filenames (not full paths)
+     */
+    virtual std::vector<std::string> ListDirectory(const std::string& path) = 0;
+
+    /**
+     * Get the absolute path for an asset (if applicable).
+     * On Android this may return empty as assets are in APK.
+     * @param path Relative path to asset
+     * @return Absolute path or empty string
+     */
+    virtual std::string GetAbsolutePath(const std::string& path) = 0;
+};
+
+using AssetInterfacePtr = std::shared_ptr<IAssetInterface>;
+
+} // namespace mosis

core/include/mosis/platform/filesystem_interface.h

@@ -0,0 +1,98 @@
+#pragma once
+
+#include <string>
+#include <vector>
+#include <memory>
+#include <functional>
+
+namespace mosis {
+
+/**
+ * Platform-agnostic interface for filesystem operations.
+ * Used for app data storage, not assets.
+ */
+class IFilesystemInterface {
+public:
+    virtual ~IFilesystemInterface() = default;
+
+    /**
+     * Get the base data directory for apps.
+     * Android: /data/data/com.omixlab.mosis/files/
+     * Desktop: ./data/ or configurable
+     */
+    virtual std::string GetDataRoot() = 0;
+
+    /**
+     * Get the apps installation directory.
+     * Contains installed app packages.
+     */
+    virtual std::string GetAppsDirectory() = 0;
+
+    /**
+     * Get app-specific data directory.
+     * @param app_id Application ID (e.g., "com.example.app")
+     */
+    virtual std::string GetAppDataDirectory(const std::string& app_id) = 0;
+
+    /**
+     * Get app-specific cache directory.
+     */
+    virtual std::string GetAppCacheDirectory(const std::string& app_id) = 0;
+
+    /**
+     * Create directory if it doesn't exist.
+     * @return true on success
+     */
+    virtual bool CreateDirectory(const std::string& path) = 0;
+
+    /**
+     * Check if path exists.
+     */
+    virtual bool Exists(const std::string& path) = 0;
+
+    /**
+     * Check if path is a directory.
+     */
+    virtual bool IsDirectory(const std::string& path) = 0;
+
+    /**
+     * Remove file or directory.
+     * @param recursive If true, remove directory contents
+     */
+    virtual bool Remove(const std::string& path, bool recursive = false) = 0;
+
+    /**
+     * Read file contents.
+     */
+    virtual std::vector<uint8_t> ReadFile(const std::string& path) = 0;
+
+    /**
+     * Write file contents.
+     */
+    virtual bool WriteFile(const std::string& path, const std::vector<uint8_t>& data) = 0;
+
+    /**
+     * List directory contents.
+     */
+    virtual std::vector<std::string> ListDirectory(const std::string& path) = 0;
+
+    /**
+     * Get file size.
+     * @return Size in bytes, or -1 if not found
+     */
+    virtual int64_t GetFileSize(const std::string& path) = 0;
+
+    /**
+     * Copy file.
+     */
+    virtual bool CopyFile(const std::string& src, const std::string& dst) = 0;
+
+    /**
+     * Move/rename file.
+     */
+    virtual bool MoveFile(const std::string& src, const std::string& dst) = 0;
+};
+
+using FilesystemInterfacePtr = std::shared_ptr<IFilesystemInterface>;
+
+} // namespace mosis