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/keybindings.el b/modules/keybindings.el
index 462fde24..6e8adeac 100644
--- a/modules/keybindings.el
+++ b/modules/keybindings.el
@@ -3,6 +3,17 @@
 ;;
 ;;; Commentary:
 ;;
+;; Layer: 1 (Foundation).
+;; Category: F/C.
+;; Load shape: eager.
+;; Eager reason: owns `cj/custom-keymap' and the global C-; prefix that feature
+;;   modules register into; must exist before they load.
+;; Top-level side effects: defines `cj/custom-keymap'/`cj/jump-map', binds
+;;   global keys (C-;, C-z, and others), registers which-key labels after-load.
+;; Runtime requires: user-constants (currently eval-when-compile only),
+;;   which-key, free-keys.
+;; Direct test load: conditional (binds global keys; needs user-constants).
+;;
 ;; Global keybinding configuration and custom keymap framework.
 ;;
 ;; Main features include: