build: clean up gitignore and remove empty gitmodules

Problem: .gitignore contained 48 lines of C/shared-object boilerplate
irrelevant to a Lua Neovim plugin. .gitmodules was tracked but empty.

Solution: replace .gitignore with minimal entries covering only files
this project actually produces. Delete the vestigial .gitmodules.

.gitignore

@@ -1,47 +1,12 @@
-# Compiled Lua sources
+doc/tags
-luac.out
+*.log
-
+.*cache*
-# luarocks build files
+CLAUDE.md
-*.src.rock
+.claude/
-*.zip
+node_modules/
-*.tar.gz
-
-# Object files
-*.o
-*.os
-*.ko
-*.obj
-*.elf
-
-# Precompiled Headers
-*.gch
-*.pch
-
-# Libraries
-*.lib
-*.a
-*.la
-*.lo
-*.def
-*.exp
-
-# Shared objects (inc. Windows DLLs)
-*.dll
-*.so
-*.so.*
-*.dylib
-
-# Executables
-*.exe
-*.out
-*.app
-*.i*86
-*.x86_64
-*.hex
-
 .direnv/
 .envrc
-doc/tags
+venv/
-scripts/benchmark.nvim
 perf/tmp/
+scripts/benchmark.nvim
 profile.json