fix: replace unsafe env::set_var with thread-safe OnceLock

Resolves intermittent STATUS_HEAP_CORRUPTION on Windows by using a static OnceLock map instead of mutating the global OS environment block.

server/src/state.rs

@@ -235,7 +235,7 @@ impl MemoryState {
 
     pub fn modify_graph<F: FnOnce(&mut KnowledgeGraph)>(&self, update_fn: F) {
         self.graph.modify(update_fn);
-        let threshold: usize = std::env::var("MCP_MEMORY_CONDENSE_THRESHOLD")
+        let threshold: usize = crate::config::get_env("MCP_MEMORY_CONDENSE_THRESHOLD")
             .unwrap_or_else(|_| "100".to_string())
             .parse()
             .unwrap_or(100);