Add full test suite with unit, integration, and E2E smoke tests.

Introduce test.bat orchestrating Go/Vitest/Playwright phases, expand coverage across server, agent, and dashboard, and document in tests/README.md.

server/internal/db/agents_test.go

@@ -0,0 +1,71 @@
+package db
+
+import (
+	"testing"
+	"time"
+
+	"crypto-miner-server/internal/models"
+)
+
+func TestAgentCRUD(t *testing.T) {
+	d, err := New(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+
+	agent := &models.Agent{
+		ID:       "agent-test-001",
+		Name:     "lab-pc",
+		Wallet:   "48abc",
+		IP:       "192.168.1.50",
+		Version:  "1.0",
+		Status:   "online",
+		CPUCores: 8,
+		MemoryGB: 16,
+		LastSeen: time.Now(),
+	}
+	if err := d.UpsertAgent(agent); err != nil {
+		t.Fatalf("upsert: %v", err)
+	}
+
+	got, err := d.GetAgent(agent.ID)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	if got.Name != "lab-pc" {
+		t.Fatalf("name mismatch: %q", got.Name)
+	}
+
+	list, err := d.ListAgents()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(list) != 1 {
+		t.Fatalf("expected 1 agent, got %d", len(list))
+	}
+
+	if err := d.UpdateAgentMeta(agent.ID, "notes here", []string{"lab", "gpu"}); err != nil {
+		t.Fatal(err)
+	}
+	got, _ = d.GetAgent(agent.ID)
+	if got.Notes != "notes here" || len(got.Tags) != 2 {
+		t.Fatalf("meta not saved: notes=%q tags=%v", got.Notes, got.Tags)
+	}
+}
+
+func TestGetFleetStatsEmpty(t *testing.T) {
+	d, err := New(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+
+	stats, err := d.GetFleetStats()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stats.TotalAgents != 0 {
+		t.Fatalf("expected 0 agents, got %d", stats.TotalAgents)
+	}
+}