Add .gitignore file

This commit introduces a .gitignore file to exclude build artifacts and
temporary files from version control.
Specifically, it ignores the 'target' directory (where Rust builds
output), new snapshot files from tests (`*.snap.new`), and the
`repomix-output.xml` file.

.gitignore

@@ -0,0 +1,3 @@
+/target
+*.snap.new
+repomix-output.xml

server/.claudeignore

@@ -0,0 +1,3 @@
+*.snap
+*.snap.new
+target/