feat: Credits-System mit Verbrauchsanzeige im User-Dropdown

- DB-Migration: credits_total/credits_used/cost_per_credit auf licenses, token_usage_monthly Tabelle
- Orchestrator: Monatliche Token-Aggregation + Credits-Abzug nach Refresh
- Auth: Credits-Daten im /me Endpoint + Bugfix fehlende Klammer in get()
- Frontend: Credits-Balken im User-Dropdown mit Farbwechsel

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/static/js/app.js

@@ -466,6 +466,32 @@ const App = {
                 licInfoEl.textContent = label;
             }
 
+            // Credits-Anzeige im Dropdown
+            const creditsSection = document.getElementById('credits-section');
+            if (creditsSection && user.credits_total) {
+                creditsSection.style.display = 'block';
+                const bar = document.getElementById('credits-bar');
+                const remainingEl = document.getElementById('credits-remaining');
+                const totalEl = document.getElementById('credits-total');
+                
+                const remaining = user.credits_remaining || 0;
+                const total = user.credits_total || 1;
+                const percentUsed = user.credits_percent_used || 0;
+                const percentRemaining = Math.max(0, 100 - percentUsed);
+                
+                remainingEl.textContent = remaining.toLocaleString('de-DE');
+                totalEl.textContent = total.toLocaleString('de-DE');
+                bar.style.width = percentRemaining + '%';
+                
+                // Farbwechsel je nach Verbrauch
+                bar.classList.remove('warning', 'critical');
+                if (percentUsed > 80) {
+                    bar.classList.add('critical');
+                } else if (percentUsed > 50) {
+                    bar.classList.add('warning');
+                }
+            }
+
             // Dropdown Toggle
             const userBtn = document.getElementById('header-user-btn');
             const userDropdown = document.getElementById('header-user-dropdown');