Add Claude Code hooks and new-credential skill

Hooks:
- PreToolUse: block direct edits to credential files (99-claude, etc.)
- PostToolUse: auto-run shellcheck after editing bash.d scripts

Skill:
- /new-credential: scaffolds a credential file pair (.example template +
  real file), adds to .gitignore, sets permissions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/settings.json

@@ -0,0 +1,26 @@
+{
+  "hooks": {
+    "PreToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/block-credential-edit.sh"
+          }
+        ]
+      }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/shellcheck-on-edit.sh"
+          }
+        ]
+      }
+    ]
+  }
+}