feat: declare aoe config as a shared module

Vendors config.toml and moves the package into common/programs/aoe, so
any host that wants aoe imports one thing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

home/common/programs/aoe/default.nix

@@ -0,0 +1,20 @@
+{
+  pkgs,
+  inputs,
+  ...
+}:
+# Agent of Empires: the agent session manager. Import this on any host that
+# wants it — it brings both the package and the shared settings.
+{
+  home.packages = [ inputs.agent-of-empires.packages.${pkgs.system}.default ];
+
+  # mutableFiles, not xdg.configFile: aoe rewrites this file itself (it keeps
+  # .bak-<epoch> copies), so a read-only store symlink would break it. The copy
+  # is change-detected — activation aborts and tells you to bring edits back
+  # here rather than silently reverting them.
+  #
+  # Only config.toml. The rest of ~/.config/agent-of-empires is per-machine
+  # state (state.toml, projects.json, tui-*, locks) or secret
+  # (serve.saved_passphrase).
+  home.mutableFiles.".config/agent-of-empires/config.toml".source = ./config.toml;
+}