chore: remove committed binaries, session files, empty dirs

Remove api/testdata/ from tracking. Update .gitignore with broader
patterns: **/sessions.db, **/testdata/, proton (binary name). Remove
empty foo/ and cmd/volume/ directories.

Author: major0

.gitignore

@@ -1,8 +1,6 @@
-# If you prefer the allow list template instead of the deny list, see community template:
-# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
-#
 # Binaries for programs and plugins
 proton-cli
+proton
 *.exe
 *.exe~
 *.dll
@@ -15,7 +13,7 @@ proton-cli
 # Output of the go coverage tool, specifically when used with LiteIDE
 *.out
 
-# Dependency directories (remove the comment below to include it)
+# Dependency directories
 # vendor/
 
 # Go workspace file
@@ -26,12 +24,13 @@ go.work.sum
 .env
 
 # Session data (should live in XDG_CONFIG_HOME, not the repo)
-proton/sessions.db
-proton/config.yaml
-proton/cache.yaml
+**/sessions.db
 
 # Test failure data
-proton/testdata/
+**/testdata/
 
 # WIP files
 *.wip
+
+# Empty placeholder directories
+foo/