security: harden gitignore and add config example files [v1.3.7]

- Expanded .gitignore: root venv, npx_cache, AI metadata (.remember, .claude),
  data/ (SQLite DB), frontend/config/, frontend/public/icons/, certificates,
  docker-compose.override.yml
- Removed backend/config/ldap_config.json from git tracking (contains real IPs/credentials)
- Added backend/config/ldap_config.json.example with placeholder template
- Updated backend/.env.example: added JWT_SECRET_KEY, ALLOWED_ORIGINS, DATA_DIR, LOGS_DIR

backend/config/ldap_config.json

@@ -1 +0,0 @@
-{"ldap_enabled": true, "server_uri": "ldap://192.168.84.107:3890", "base_dn": "dc=example,dc=com", "user_template": "cn={username},ou=people,dc=example,dc=com", "groups_dn": "ou=groups", "use_tls": false, "role_mappings": [{"group": "inventory_admins", "role": "admin"}, {"group": "inventory_users", "role": "user"}]}

backend/config/ldap_config.json.example

@@ -0,0 +1,19 @@
+{
+  "_comment": "Copy this file to ldap_config.json and fill in real values. NEVER commit ldap_config.json to Git.",
+  "ldap_enabled": false,
+  "server_uri": "ldap://YOUR_LDAP_SERVER_IP:389",
+  "base_dn": "dc=yourdomain,dc=com",
+  "user_template": "cn={username},ou=people,dc=yourdomain,dc=com",
+  "groups_dn": "ou=groups",
+  "use_tls": false,
+  "role_mappings": [
+    {
+      "group": "inventory_admins",
+      "role": "admin"
+    },
+    {
+      "group": "inventory_users",
+      "role": "user"
+    }
+  ]
+}