docs(dashboard): document test helpers and cleanup patterns

Added comprehensive documentation of available test helpers:

Available Helpers (from test_helpers.go):
- setupTestServer(t) - Creates test server with auto cleanup via t.Cleanup()
- loginTestUser(t, ts, db) - Logs in admin user, returns JWT token
- loginRegularUser(t, ts, db) - Logs in regular user, returns JWT token
- setupDeviceTest(t) - Creates server + user + device + library
- getTestUserID(t, db) - Gets/creates admin test user UUID
- getRegularUserID(t, db) - Gets/creates regular test user UUID

TestServerSetup Structure:
- Server *httptest.Server
- DB *database.Queries
- DBPool *pgxpool.Pool
- Config *config.Config
- ConnManager, QueueProcessor
- Auto cleanup via t.Cleanup()

Cleanup Pattern:
- Automatic cleanup registered in setupTestServer()
- Runs even if test fails or panics
- Order: queue processor → connection manager → HTTP server → database pool
- No manual defer setup.Close() needed

Updated Integration Tests:
- Added proper imports (database, uuid, pgtype)
- Documented available helpers
- Removed custom helpers that don't exist
- Uses existing project patterns

This ensures developers know what helpers are available and how to use them correctly.

CAROUSEL_DASHBOARD_PLAN.md

@@ -2142,6 +2142,35 @@ func TestGetSectionViewAllURL(t *testing.T) {
 
 **COMPLIANCE**: Integration tests in `cmd/server/tests/`, using `setupTestServer` helper
 
+**Available Test Helpers (from `test_helpers.go`):**
+
+| Helper | Purpose | Returns |
+|--------|---------|---------|
+| `setupTestServer(t)` | Creates test server with auto cleanup | `*TestServerSetup` |
+| `loginTestUser(t, ts, db)` | Logs in admin user (role: admin) | JWT token string |
+| `loginRegularUser(t, ts, db)` | Logs in regular user (role: user) | JWT token string |
+| `setupDeviceTest(t)` | Creates server + user + device + library | `*TestDeviceSetup` |
+| `getTestUserID(t, db)` | Gets/creates admin test user | `uuid.UUID` |
+| `getRegularUserID(t, db)` | Gets/creates regular test user | `uuid.UUID` |
+
+**Cleanup Pattern:**
+- `setupTestServer()` automatically registers `t.Cleanup()` 
+- Cleanup runs even if test fails or panics
+- No manual `defer setup.Close()` needed
+
+**TestServerSetup Contains:**
+```go
+type TestServerSetup struct {
+    Server         *httptest.Server  // Test HTTP server
+    DB             *database.Queries // Database queries
+    DBPool         *pgxpool.Pool     // Database pool
+    Config         *config.Config    // Test configuration
+    ConnManager    *wsync.ConnectionManager
+    QueueProcessor *wsync.SyncQueueProcessor
+    // ... auto cleanup via t.Cleanup()
+}
+```
+
 **File: `cmd/server/tests/dashboard_test.go`** (new file)
 
 ```go
@@ -2149,10 +2178,14 @@ package main
 
 import (
     "bytes"
+    "context"
     "encoding/json"
     "net/http"
     "testing"
 
+    "bookhoard/internal/database"
+    "github.com/google/uuid"
+    "github.com/jackc/pgx/v5/pgtype"
     "github.com/stretchr/testify/assert"
     "github.com/stretchr/testify/require"
 )
@@ -2397,6 +2430,7 @@ func TestDashboardSSR_Page(t *testing.T) {
 
 // Helper functions for dashboard tests
 
+// updateDashboardPreferences saves dashboard preferences for testing
 func updateDashboardPreferences(t *testing.T, db *database.Queries, userID, libraryID uuid.UUID, prefs map[string]interface{}) {
     hiddenSections := prefs["hidden_sections"].([]string)
     sectionOrder := prefs["section_order"].([]string)
@@ -2410,24 +2444,41 @@ func updateDashboardPreferences(t *testing.T, db *database.Queries, userID, libr
     })
     require.NoError(t, err, "Failed to update dashboard preferences")
 }
-
-func getUserUUIDFromToken(t *testing.T, db *database.Queries, token string) uuid.UUID {
-    // Parse JWT and extract user ID
-    // This would use the same logic as the JWT middleware
-    // For now, return test user UUID from database
-    user, err := db.GetUserByEmail(context.Background(), "testuser@example.com")
-    require.NoError(t, err)
-
-    return uuid.UUID(user.ID.Bytes[0:16])
-}
-
-func parseUUID(t *testing.T, uuidStr string) uuid.UUID {
-    id, err := uuid.Parse(uuidStr)
-    require.NoError(t, err)
-    return id
-}
 ```
 
+**Key Helper Functions Available:**
+
+From `test_helpers.go`:
+
+```go
+// setupTestServer creates complete test environment with auto cleanup
+setup := setupTestServer(t)
+// No manual cleanup needed - t.Cleanup() registered automatically
+
+// loginTestUser - logs in admin user (testuser@example.com)
+adminToken := loginTestUser(t, setup.Server, setup.DB)
+
+// loginRegularUser - logs in regular user (testregularuser@example.com)
+userToken := loginRegularUser(t, setup.Server, setup.DB)
+
+// setupDeviceTest - creates server + user + device + library
+deviceSetup := setupDeviceTest(t)
+deviceSetup.CreateLibrary(t, "My Library", "ebooks")
+deviceSetup.CreateDevice(t, "Kindle", "kindle", "kindle-123")
+
+// getTestUserID - gets/creates admin test user UUID
+adminUUID := getTestUserID(t, setup.DB)
+
+// getRegularUserID - gets/creates regular test user UUID
+userUUID := getRegularUserID(t, setup.DB)
+```
+
+**Cleanup Pattern:**
+- ✅ Automatic via `t.Cleanup()` in `setupTestServer()`
+- ✅ Runs even if test fails or panics
+- ✅ No manual `defer setup.Close()` needed
+- ✅ Cleans up: queue processor → connection manager → HTTP server → database pool
+
 **Key Points**:
 - ✅ Integration tests in `cmd/server/tests/`
 - ✅ Uses `setupTestServer(t)` helper (from `test_helpers.go`)