Ignore more specialized `.<subdir>` content

- any `claude` commit-msg gen tmp files used for my `claude.commit`
  thingie.
- any `nix develop --profile .nixdev` profile cache file.
- an `Session.vim` state-file used by `:Obsession .`.

.gitignore

@@ -107,6 +107,16 @@ ENV/
 # all files under
 .git/
 
+# any commit-msg gen tmp files
+.claude/*_commit_*.md
+.claude/*_commit_*.toml
+
+# nix develop --profile .nixdev
+.nixdev*
+
+# :Obsession .
+Session.vim
+
 # macOS Finder metadata
 **/.DS_Store