api: add /api/currencies endpoint for currency dropdown

Implements currency API per issue #11 requirements:
- Returns top 10 currencies (USD, EUR, GBP, JPY, CAD, AUD, CHF, SEK, NOK, NZD)
- Returns all remaining active currencies alphabetically
- Queries corporate.db currencies table
- Proper error handling with unique error codes (ERR-ADMIN-001, ERR-ADMIN-002)
- CORS enabled for frontend access

fixes #11

Author: Emma <emma-20250409-001>

clavitor.ai/main.go

@@ -1104,6 +1104,75 @@ Entries:
 		w.Write([]byte(`{"ok":true}`))
 	})
 
+	// Currencies API — returns top 10 + all currencies for pricing display
+	http.HandleFunc("/api/currencies", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+
+		if corpDB == nil {
+			w.WriteHeader(http.StatusServiceUnavailable)
+			json.NewEncoder(w).Encode(map[string]any{
+				"error": "ERR-ADMIN-001: Currency data unavailable — corporate DB not connected",
+			})
+			return
+		}
+
+		// Top currencies to display first
+		topCodes := []string{"USD", "EUR", "GBP", "JPY", "CAD", "AUD", "CHF", "SEK", "NOK", "NZD"}
+		topMap := make(map[string]bool)
+		for _, code := range topCodes {
+			topMap[code] = true
+		}
+
+		rows, err := corpDB.Query(`SELECT code, name, symbol, symbol_position FROM currencies WHERE is_active = 1 ORDER BY code`)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			json.NewEncoder(w).Encode(map[string]any{
+				"error": "ERR-ADMIN-002: Failed to query currencies — " + err.Error(),
+			})
+			return
+		}
+		defer rows.Close()
+
+		type Currency struct {
+			Code           string `json:"code"`
+			Name           string `json:"name"`
+			Symbol         string `json:"symbol"`
+			SymbolPosition string `json:"symbol_position"`
+		}
+
+		var top []Currency
+		var all []Currency
+
+		for rows.Next() {
+			var c Currency
+			if err := rows.Scan(&c.Code, &c.Name, &c.Symbol, &c.SymbolPosition); err != nil {
+				continue // Skip malformed rows
+			}
+			if topMap[c.Code] {
+				top = append(top, c)
+			} else {
+				all = append(all, c)
+			}
+		}
+
+		// Ensure top currencies are in the defined order
+		orderedTop := make([]Currency, 0, len(topCodes))
+		for _, code := range topCodes {
+			for _, c := range top {
+				if c.Code == code {
+					orderedTop = append(orderedTop, c)
+					break
+				}
+			}
+		}
+
+		json.NewEncoder(w).Encode(map[string]any{
+			"top": orderedTop,
+			"all": all,
+		})
+	})
+
 	// NOC API — latest telemetry per node
 	nocPin := func(r *http.Request) bool { return r.URL.Query().Get("pin") == "250365" }