refactor(tauri): use magnotia_core::hardware::vulkan_loader_available

Delete the local duplicate fn and libloading dependency from src-tauri;
import the canonical implementation from magnotia-core::hardware instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/Cargo.toml

@@ -57,11 +57,6 @@ serde_json = "1"
 tokio = { version = "1", features = ["rt", "sync"] }
 arboard = "3.6.1"
 
-# Runtime shared-library probe for the Vulkan loader (active compute
-# device detection, brief item #1). We do not call any vulkan symbols
-# — we only need to answer "is libvulkan resolvable from the loader's
-# default search path right now?".
-libloading = "0.8"
 
 # SqlitePool is named directly from src-tauri/src/lib.rs (the AppState
 # stores it). Must be unconditional, not Linux-only — naming a type from