feat(claude-code): manage the user's global config in the Module

Bring the declarative half of ~/.claude into modules/claude-code and apply
it when the Module is enabled: the global agent instructions (context =
./CLAUDE.md), the skills tree (skills = ./skills), the attention-bell hook,
and settings.json (model = opus plus the Stop/Notification/SessionStart
hook wiring).

Runtime state (projects, plugins, cache, history, sessions) and the
.credentials.json secret are left out, so login survives rebuilds and no
secret enters the repo. Verified against the built home-files that
~/.claude/{CLAUDE.md,settings.json,skills,hooks/attention-bell.sh} are
generated, the hook executable.

modules/claude-code/skills/setup-skills/hash-dir.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+# Deterministic recursive hash of a directory's file contents.
+#
+# Hashes relative paths, not absolute ones, so two directories with
+# identical contents hash identically regardless of where they live on
+# disk (needed to compare a project's copied skill against the library
+# source it was copied from).
+#
+# Usage: hash-dir.sh <directory>
+set -euo pipefail
+
+if [ $# -ne 1 ]; then
+  echo "Usage: hash-dir.sh <directory>" >&2
+  exit 1
+fi
+
+dir="$1"
+if [ ! -d "$dir" ]; then
+  echo "Not a directory: $dir" >&2
+  exit 1
+fi
+
+(cd "$dir" && find . -type f -print0 | sort -z | xargs -0 -r sha256sum) | sha256sum | awk '{print $1}'