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

@@ -106,3 +106,13 @@ 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