docs(load-graph): seed module inventory and annotate foundation headers

I started the init.el load-graph classification with the foundation batch. I added docs/design/module-inventory.org as the living per-module inventory and annotated the seven foundation modules (system-lib, user-constants, host-environment, system-defaults, keyboard-compat, keybindings, config-utilities) with the load-graph header contract: layer, category, load shape, eager reason, top-level side effects, runtime requires, and direct-test-load safety.

I changed no load order, so init.el keeps its current eager order. The inventory records one hidden dependency for Phase 2: system-defaults uses host-environment and user-constants symbols at load while declaring them eval-when-compile, so the compiled module cannot load standalone.

1 files changed, 11 insertions, 0 deletions

diff --git a/modules/host-environment.el b/modules/host-environment.el
index e98877660..0afb39cbf 100644
--- a/modules/host-environment.el
+++ b/modules/host-environment.el
@@ -2,6 +2,17 @@
 ;; author Craig Jennings <c@cjennings.net>
 
 ;;; Commentary:
+;;
+;; Layer: 1 (Foundation).
+;; Category: F/L.
+;; Load shape: eager.
+;; Eager reason: host predicates (laptop-p, battery presence) used by other
+;;   foundation/UI modules deciding behavior at startup.
+;; Top-level side effects: none.
+;; Runtime requires: none (battery loaded on demand; declared via
+;;   `declare-function').
+;; Direct test load: yes (pure predicates; batch-safe).
+;;
 ;; Convenience functions to report about the host environment
 ;;
 ;;; Code: