feat(snippets): add snippets entity, crud, and auto-browser-per-run

- add Snippet entity with name, description, code; full CRUD backend
- add snippets pages (list, create, edit, detail) and nav entry
- add runSnippet helper in code-executor using new Function with args array
- add result param to execute() so validateCode can access exec output
- remove sessionName from steps; each run now spawns its own fresh browser
- fix waitForURL race by polling localStorage for token instead

client/src/i18n/locales/en.json

@@ -5,11 +5,13 @@
     "not_found_environment": "Environment {{id}} does not exist or has been deleted.",
     "not_found_credential": "Credential {{id}} does not exist or has been deleted.",
     "not_found_scenario": "Scenario {{id}} does not exist or has been deleted.",
+    "not_found_snippet": "Snippet {{id}} does not exist or has been deleted.",
     "generic": "Something went wrong. Please try again."
   },
   "nav": {
     "environments": "Environments",
     "credentials": "Credentials",
+    "snippets": "Snippets",
     "keys": "Keys",
     "sessions": "Sessions",
     "scenarios": "Scenarios",
@@ -199,5 +201,33 @@
     "log_level": "Level",
     "log_message": "Message",
     "log_time": "Time"
+  },
+  "snippets": {
+    "title": "Snippets",
+    "empty": "No snippets yet.",
+    "loading": "Loading…",
+    "menu_label": "Snippet options",
+    "action_edit": "Edit",
+    "action_delete": "Delete",
+    "action_add": "Add snippet",
+    "action_save": "Create",
+    "action_update": "Save changes",
+    "action_cancel": "Cancel",
+    "create_title": "New Snippet",
+    "edit_title": "Edit Snippet",
+    "form_name": "Name",
+    "form_name_placeholder": "e.g. clickLoginButton",
+    "form_name_required": "Name is required",
+    "form_description": "Description",
+    "form_description_placeholder": "What does this snippet do?",
+    "form_code": "Code",
+    "form_code_placeholder": "await page.click('#login-btn');",
+    "form_code_required": "Code is required",
+    "field_id": "ID",
+    "field_name": "Name",
+    "field_description": "Description",
+    "field_created": "Created",
+    "field_updated": "Updated",
+    "section_code": "Code"
   }
 }