Stop tracking local OMX session state

The repository had accumulated committed .omx runtime artifacts even though they are local coordination state, not durable source inputs. Adding .omx to gitignore and removing the tracked entries keeps future OMX activity out of git while preserving the files locally for the current session.

Constraint: OMX continuously rewrites files under .omx during a session, so keeping them tracked leaves the worktree perpetually dirty
Rejected: Keep tracking .omx and manually clean it before commits | too fragile and immediately regresses on the next OMX write
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Do not re-add .omx contents unless the repo intentionally decides to version OMX runtime state as product artifacts
Tested: git check-ignore -v .omx/state/skill-active-state.json .omx/notepad.md
Tested: git status --short
Not-tested: Project build/test suite (ignore-rule change only)

Author: Hongwei-MB

.gitignore

@@ -191,6 +191,7 @@ publish/
 *.pubxml
 *.publishproj
 .worktrees/
+.omx/
 
 # Microsoft Azure Web App publish settings. Comment the next line if you want to
 # checkin your Azure Web App publish settings, but sensitive information contained