feat(web): 增强任务治理与系统诊断能力

新增任务持久化、筛选分页、取消任务、健康检查与 AI 输入校验，并完善前端历史管理交互与容错重试机制。补充对应单元测试，提升系统稳定性和可运维性。

src/main/java/com/svnlog/web/service/HealthService.java

@@ -0,0 +1,81 @@
+package com.svnlog.web.service;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.time.Instant;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.springframework.stereotype.Service;
+
+import com.svnlog.web.model.TaskInfo;
+import com.svnlog.web.model.TaskStatus;
+
+@Service
+public class HealthService {
+
+    private final OutputFileService outputFileService;
+    private final SettingsService settingsService;
+    private final TaskService taskService;
+
+    public HealthService(OutputFileService outputFileService,
+                         SettingsService settingsService,
+                         TaskService taskService) {
+        this.outputFileService = outputFileService;
+        this.settingsService = settingsService;
+        this.taskService = taskService;
+    }
+
+    public Map<String, Object> basicHealth() {
+        final Map<String, Object> response = new HashMap<String, Object>();
+        response.put("status", "ok");
+        response.put("timestamp", Instant.now().toString());
+        return response;
+    }
+
+    public Map<String, Object> detailedHealth() throws IOException {
+        final Map<String, Object> result = new HashMap<String, Object>();
+        final Map<String, Object> settings = settingsService.getSettings();
+        final Path outputRoot = outputFileService.getOutputRoot();
+
+        final boolean outputDirWritable = ensureWritable(outputRoot);
+        int running = 0;
+        int failed = 0;
+        int cancelled = 0;
+        for (TaskInfo task : taskService.getTasks()) {
+            if (task.getStatus() == TaskStatus.RUNNING || task.getStatus() == TaskStatus.PENDING) {
+                running++;
+            }
+            if (task.getStatus() == TaskStatus.FAILED) {
+                failed++;
+            }
+            if (task.getStatus() == TaskStatus.CANCELLED) {
+                cancelled++;
+            }
+        }
+
+        result.put("status", "ok");
+        result.put("timestamp", Instant.now().toString());
+        result.put("outputDir", outputRoot.toString());
+        result.put("outputDirWritable", outputDirWritable);
+        result.put("apiKeyConfigured", Boolean.TRUE.equals(settings.get("apiKeyConfigured")));
+        result.put("taskTotal", taskService.getTasks().size());
+        result.put("taskRunning", running);
+        result.put("taskFailed", failed);
+        result.put("taskCancelled", cancelled);
+        return result;
+    }
+
+    private boolean ensureWritable(Path outputRoot) {
+        try {
+            Files.createDirectories(outputRoot);
+            final Path probe = outputRoot.resolve(".health-probe");
+            Files.write(probe, "ok".getBytes("UTF-8"));
+            Files.deleteIfExists(probe);
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }
+}