Fix audit logs and issue reports pages, rename Issues to Tasks

修復稽核日誌與任務報表頁面，並將「問題」改名為「任務」

## Changes 變更內容

### Bug Fixes 錯誤修復
1. Fixed audit logs page 500 error
   - Added missing $auditableTypes variable to controller
   - Changed $events to $actions in view
   - Added description and ip_address columns to audit_logs table
   - Updated AuditLog model fillable array

2. Fixed issue reports page SQLite compatibility errors
   - Replaced MySQL NOW() function with Laravel now() helper
   - Replaced TIMESTAMPDIFF() with PHP-based date calculation
   - Fixed request->date() default value handling

### Feature Changes 功能變更
3. Renamed "Issues" terminology to "Tasks" throughout the system
   - Updated navigation menus (Admin: Issues → Admin: Tasks)
   - Updated all issue-related views to use task terminology
   - Changed Chinese labels from "問題" to "任務"
   - Updated dashboard, issue tracker, and reports pages

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/Http/Controllers/IssueReportsController.php

@@ -12,8 +12,8 @@ class IssueReportsController extends Controller
     public function index(Request $request)
     {
         // Date range filter (default: last 30 days)
-        $startDate = $request->date('start_date', now()->subDays(30));
-        $endDate = $request->date('end_date', now());
+        $startDate = $request->date('start_date') ?? now()->subDays(30);
+        $endDate = $request->date('end_date') ?? now();
 
         // Overview Statistics
         $stats = [
@@ -63,11 +63,12 @@ class IssueReportsController extends Controller
             ->get();
 
         // Assignee Performance
+        $now = now();
         $assigneePerformance = User::select('users.id', 'users.name')
             ->leftJoin('issues', 'users.id', '=', 'issues.assigned_to_user_id')
             ->selectRaw('count(issues.id) as total_assigned')
             ->selectRaw('sum(case when issues.status = ? then 1 else 0 end) as completed', [Issue::STATUS_CLOSED])
-            ->selectRaw('sum(case when issues.due_date < NOW() and issues.status != ? then 1 else 0 end) as overdue', [Issue::STATUS_CLOSED])
+            ->selectRaw('sum(case when issues.due_date < ? and issues.status != ? then 1 else 0 end) as overdue', [$now, Issue::STATUS_CLOSED])
             ->groupBy('users.id', 'users.name')
             ->having('total_assigned', '>', 0)
             ->orderByDesc('total_assigned')
@@ -101,9 +102,15 @@ class IssueReportsController extends Controller
             ->get();
 
         // Average Resolution Time (days)
-        $avgResolutionTime = Issue::whereNotNull('closed_at')
-            ->selectRaw('avg(TIMESTAMPDIFF(DAY, created_at, closed_at)) as avg_days')
-            ->value('avg_days');
+        $closedIssues = Issue::whereNotNull('closed_at')
+            ->select('created_at', 'closed_at')
+            ->get();
+
+        $avgResolutionTime = $closedIssues->isNotEmpty()
+            ? $closedIssues->avg(function ($issue) {
+                return $issue->created_at->diffInDays($issue->closed_at);
+            })
+            : null;
 
         // Recent Activity (last 10 issues)
         $recentIssues = Issue::with(['creator', 'assignee'])