Add application-scoped snippets with global fallback and scope-aware sync

src/core.h

@@ -32,7 +32,10 @@ struct Snippet
 {
     std::wstring trigger, text;
     std::wstring id;
+    std::vector<std::wstring> apps; // Empty means everywhere; executable names without .exe.
 };
+std::wstring snippetAppName(std::wstring);
+int snippetAppPriority(const Snippet &, const std::wstring &process);
 std::wstring snippetId(const Snippet &);
 std::wstring newSnippetId();
 struct Template