feat(mobile-app): improve empty state display for offline settlement deduction

When there are no settlement records to deduct, show a more informative message:
- If user has balance from deposits/transfers: explain it's not from earnings
- If user has no balance: explain there are no settlement records

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/pending_actions/presentation/pages/special_deduction_page.dart

@@ -613,13 +613,36 @@ class _SpecialDeductionPageState extends ConsumerState<SpecialDeductionPage> {
                   color: const Color(0xFFF5F5F5),
                   borderRadius: BorderRadius.circular(8),
                 ),
-                child: const Text(
-                  '暂无待扣减的结算记录',
-                  textAlign: TextAlign.center,
-                  style: TextStyle(
-                    fontSize: 14,
-                    color: Color(0xFF999999),
-                  ),
+                child: Column(
+                  children: [
+                    const Icon(
+                      Icons.info_outline,
+                      color: Color(0xFF999999),
+                      size: 32,
+                    ),
+                    const SizedBox(height: 8),
+                    const Text(
+                      '暂无待扣减的结算记录',
+                      textAlign: TextAlign.center,
+                      style: TextStyle(
+                        fontSize: 14,
+                        fontWeight: FontWeight.w500,
+                        color: Color(0xFF666666),
+                      ),
+                    ),
+                    const SizedBox(height: 8),
+                    Text(
+                      _walletInfo != null && (_walletInfo!.balances.usdt.available) > 0
+                          ? '当前余额来自充值或转账，非收益结算，无需扣减'
+                          : '该用户没有已结算的收益记录',
+                      textAlign: TextAlign.center,
+                      style: const TextStyle(
+                        fontSize: 12,
+                        color: Color(0xFF999999),
+                        height: 1.4,
+                      ),
+                    ),
+                  ],
                 ),
               ),
           ],