Setup wizard P2: per-plugin config schema + settings-first creds

- Plugin contract gains get_config_schema(); the plugins list API returns it.
  Employees plugin declares its directory-DB fields (host/name/user + password).
- employee_connection reads host/name/user settings-first (env fallback); the
  password stays env-only.
- Setup wizard Features step renders each enabled plugin's config: non-secret
  fields save to settings; secrets are never stored - the wizard emits .env
  lines to paste. Fixed the plugins-list data path (data.plugins).
- Settings PUT now upserts (creates the row on first write) so plugin-config
  keys can be saved without pre-seeding.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

shopdb/utils/employee_db.py

@@ -9,12 +9,28 @@ import pymysql
 from flask import current_app
 
 
+def _setting_or_config(setting_key, config_key):
+    """Non-secret config: a saved Setting wins, else the env-backed app config.
+
+    Lets the setup wizard edit host/name/user without touching .env, while the
+    password stays env-only.
+    """
+    from shopdb.core.models import Setting
+    try:
+        row = Setting.query.filter_by(key=setting_key).first()
+        if row and row.value:
+            return row.value
+    except Exception:
+        pass
+    return current_app.config[config_key]
+
+
 def employee_connection():
     """Open a pymysql connection to the employee directory DB."""
     return pymysql.connect(
-        host=current_app.config['EMPLOYEE_DB_HOST'],
-        user=current_app.config['EMPLOYEE_DB_USER'],
+        host=_setting_or_config('employee_db_host', 'EMPLOYEE_DB_HOST'),
+        user=_setting_or_config('employee_db_user', 'EMPLOYEE_DB_USER'),
         password=current_app.config['EMPLOYEE_DB_PASSWORD'],
-        database=current_app.config['EMPLOYEE_DB_NAME'],
+        database=_setting_or_config('employee_db_name', 'EMPLOYEE_DB_NAME'),
         cursorclass=pymysql.cursors.DictCursor,
     )