feat(core): port vulkan_loader_available from src-tauri

Adds libloading = "0.8" to magnotia-core dependencies and moves
vulkan_loader_available() into magnotia-core::hardware so non-Tauri
crates (transcription, llm) can probe the Vulkan loader without
depending on the Tauri binary. Test asserts the call completes on any
host regardless of whether libvulkan is installed.

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

crates/core/Cargo.toml

@@ -12,6 +12,7 @@ sysinfo = "0.35"
 async-trait = "0.1"
 num_cpus = "1"
 tracing = "0.1"
+libloading = "0.8"
 
 [dev-dependencies]
 tempfile = "3"

crates/core/src/hardware.rs

@@ -169,6 +169,40 @@ pub fn probe_system() -> SystemProfile {
     }
 }
 
+/// Best-effort probe for the Vulkan loader shared library.
+///
+/// whisper.cpp and llama.cpp Vulkan backends silently drop to CPU if
+/// `libvulkan.so.1` (Linux) / `vulkan-1.dll` (Windows) / the MoltenVK
+/// bundle (macOS) is missing at runtime. We probe via
+/// `libloading::Library::new`; a successful open means the loader is
+/// resolvable and we should treat the GPU path as live.
+///
+/// Moved from `src-tauri/src/commands/models.rs` so non-Tauri crates
+/// (transcription, llm) can call it without depending on the Tauri
+/// binary.
+pub fn vulkan_loader_available() -> bool {
+    #[cfg(target_os = "linux")]
+    let candidates: &[&str] = &["libvulkan.so.1", "libvulkan.so"];
+    #[cfg(target_os = "windows")]
+    let candidates: &[&str] = &["vulkan-1.dll"];
+    #[cfg(target_os = "macos")]
+    let candidates: &[&str] = &["libvulkan.1.dylib", "libMoltenVK.dylib"];
+    #[cfg(not(any(target_os = "linux", target_os = "windows", target_os = "macos")))]
+    let candidates: &[&str] = &[];
+
+    for name in candidates {
+        // SAFETY: libloading::Library::new loads a shared library and
+        // returns a handle that is dropped at the end of this
+        // iteration. We do not call any symbols, so the open-for-probe
+        // pattern is sound.
+        match unsafe { libloading::Library::new(*name) } {
+            Ok(_lib) => return true,
+            Err(_) => continue,
+        }
+    }
+    false
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -217,4 +251,11 @@ mod tests {
         #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
         assert!(!features.has_ggml_baseline());
     }
+
+    #[test]
+    fn vulkan_loader_available_does_not_panic() {
+        // We can't assert the value (depends on host's libvulkan),
+        // but we can assert the call completes.
+        let _ = vulkan_loader_available();
+    }
 }