Update project structure and configurations

_bmad/custom/.gitignore

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+*.user.toml

_bmad/custom/config.toml

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+# Team / enterprise overrides for _bmad/config.toml.
+# Committed to the repo — applies to every developer on the project.
+# Tables deep-merge over base config; keyed entries merge by key.
+# Example: override an agent descriptor, or add a new agent.
+#
+# [agents.bmad-agent-pm]
+# description = "Prefers short, bulleted PRDs over narrative drafts."