LINUS ROUND 1: Delete dead code (rust/c), generic Store[T], tests, slim main.go

- Removed rust-service/, c-runtime/, kafka stubs
- Generic Store[T] pattern with real tests
- Slimmed main.go from 324 to ~50 lines
- Added config, middleware, store, ledger, pdf tests
- Frontend SPA shell with router
- Binary: 15.5MB -> 12MB

backend/ledger/client_test.go

@@ -0,0 +1,92 @@
+package ledger
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClient_Get_Success(t *testing.T) {
+	expected := map[string]interface{}{"balance": 1000.0}
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "/api/ledger/reports/balance", r.URL.Path)
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(expected)
+	}))
+	defer server.Close()
+
+	client := &Client{baseURL: server.URL, client: &http.Client{}}
+	result, err := client.Get(context.Background(), "/api/ledger/reports/balance")
+
+	require.NoError(t, err)
+	assert.Equal(t, 1000.0, result["balance"])
+}
+
+func TestClient_Get_ServerError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	client := &Client{baseURL: server.URL, client: &http.Client{}}
+	_, err := client.Get(context.Background(), "/api/ledger/reports/balance")
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "ledger error")
+}
+
+func TestClient_Get_Unavailable(t *testing.T) {
+	client := &Client{baseURL: "http://localhost:1", client: &http.Client{}}
+	_, err := client.Get(context.Background(), "/api/ledger/reports/balance")
+
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unavailable")
+}
+
+func TestHandler_Proxy(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(map[string]string{"status": "ok"})
+	}))
+	defer server.Close()
+
+	h := &Handler{client: &Client{baseURL: server.URL, client: &http.Client{}}}
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/finance/balance", nil)
+	rr := httptest.NewRecorder()
+
+	h.Proxy(rr, req, "/api/ledger/reports/balance")
+
+	assert.Equal(t, http.StatusOK, rr.Code)
+
+	var result map[string]string
+	err := json.Unmarshal(rr.Body.Bytes(), &result)
+	require.NoError(t, err)
+	assert.Equal(t, "ok", result["status"])
+}
+
+func TestHandler_GetBalanceSheet(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "/api/ledger/reports/balance", r.URL.Path)
+		json.NewEncoder(w).Encode(map[string]int{"total": 5000})
+	}))
+	defer server.Close()
+
+	h := &Handler{client: &Client{baseURL: server.URL, client: &http.Client{}}}
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/finance/balance", nil)
+	rr := httptest.NewRecorder()
+
+	h.GetBalanceSheet(rr, req)
+
+	assert.Equal(t, http.StatusOK, rr.Code)
+
+	var result map[string]int
+	err := json.Unmarshal(rr.Body.Bytes(), &result)
+	require.NoError(t, err)
+	assert.Equal(t, 5000, result["total"])
+}