Generalize pension system: multi-country strategy pattern

- Add JSONB pension_params column to retirement_configs
- Add data JSONB column to pension_entries
- Create pension calculator strategy classes (Base, DeGrv, UsSocialSecurity, UkStatePension, FrRegimeGeneral, EsSocialSecurity)
- Update RetirementConfig model to delegate to calculators
- Make PensionEntry.current_points optional for non-points systems
- Update controller strong params (pension_params: {})
- Add Stimulus pension_system_controller for dynamic form fields
- Update views with per-country field groups and conditional points columns
- Expand i18n (EN, DE) and add ES, FR locale files
- Update fixtures and tests for new schema

Addresses review feedback from jjmata on PR #1057

app/javascript/controllers/pension_system_controller.js

@@ -0,0 +1,32 @@
+import { Controller } from "@hotwired/stimulus";
+
+// Toggles visibility of country-specific pension field groups
+// based on the selected pension system.
+//
+// Usage:
+//   <div data-controller="pension-system">
+//     <select data-pension-system-target="select" data-action="change->pension-system#toggle">
+//     <div data-pension-system-target="fields" data-pension-system-key="de_grv"> ... </div>
+//     <div data-pension-system-target="fields" data-pension-system-key="us_ss"> ... </div>
+//   </div>
+export default class extends Controller {
+  static targets = ["select", "fields"];
+
+  connect() {
+    this.toggle();
+  }
+
+  toggle() {
+    const selected = this.selectTarget.value;
+
+    this.fieldsTargets.forEach((el) => {
+      if (el.dataset.pensionSystemKey === selected) {
+        el.classList.remove("hidden");
+        el.querySelectorAll("input, select").forEach((i) => (i.disabled = false));
+      } else {
+        el.classList.add("hidden");
+        el.querySelectorAll("input, select").forEach((i) => (i.disabled = true));
+      }
+    });
+  }
+}