feat(projects): rolled-up project value (newest stage wins per deal, cumulative)

- computeValuation helper: per deal_uuid, the invoice total (installments
  summed, storno netted) wins over the quote; contracts carry no total so
  never contribute. Summed across the project's events, split by currency.
- Value column on the Project Overview list + a value/paid block in the
  cockpit header. Both gated by bills.view/quotes.view so no figure leaks.
- listProjects computes all values in two bulk queries (not per-project).
- en + de i18n; six unit assertions cover the rule's edge cases.

frontend/src/i18n/locales/de.json

@@ -3403,6 +3403,7 @@
       "name": "Projekt",
       "customer": "Kunde",
       "events": "Events",
+      "value": "Wert",
       "status": "Status",
       "updated": "Aktualisiert"
     },
@@ -3410,6 +3411,10 @@
       "label": "Projekt",
       "none": "Kein Projekt"
     },
+    "value": {
+      "label": "Projektwert",
+      "paid": "bezahlt"
+    },
     "events": {
       "title": "Events",
       "none": "Diesem Projekt sind noch keine Events zugeordnet.",

frontend/src/i18n/locales/en.json

@@ -3403,6 +3403,7 @@
       "name": "Project",
       "customer": "Customer",
       "events": "Events",
+      "value": "Value",
       "status": "Status",
       "updated": "Updated"
     },
@@ -3410,6 +3411,10 @@
       "label": "Project",
       "none": "No project"
     },
+    "value": {
+      "label": "Project value",
+      "paid": "paid"
+    },
     "events": {
       "title": "Events",
       "none": "No events grouped under this project yet.",