fix: validate config after PostLoad hooks

Re-run validator after PostLoad, return errors from RootDir, and add Config
alias for C(). Hooks receive *T instead of *Manager.

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

@@ -0,0 +1,5 @@
+# Test coverage
+coverage.out
+coverage.html
+
+*.test