fix: Update tach.toml to use dependency-group format

- Replace incorrect [external] and [tool.tach.dependencies] with [dependency-group.ci]
- Keep existing module configurations intact
- Fix 'Group ci is not defined' error

Part of #461

Co-Authored-By: Alex Reibman <meta.alex.r@gmail.com>

tach.toml

@@ -25,7 +25,7 @@ depends_on = []
 path = "agentops.log_config"
 depends_on = []
 
-[tool.tach.dependencies]
-ci = [
-    "tach~=0.9",
+[dependency-group.ci]
+dependencies = [
+    "tach~=0.9"
 ]