refactor: consolidate nvim crates, extract server library, and update workspace dependencies

Cargo.lock

@@ -2355,7 +2355,7 @@ dependencies = [
 ]
 
 [[package]]
-name = "mcp-memory-linux-nvim"
+name = "mcp-memory-nvim"
 version = "1.0.0"
 dependencies = [
  "nvim-core",
@@ -2429,15 +2429,6 @@ dependencies = [
  "tracing-subscriber",
 ]
 
-[[package]]
-name = "mcp-memory-win-nvim"
-version = "1.0.0"
-dependencies = [
- "nvim-core",
- "serde_json",
- "tokio",
-]
-
 [[package]]
 name = "mcp-stdio"
 version = "1.0.0"