feat: implement settings page and config management

src/main/java/com/openisle/controller/AdminConfigController.java

@@ -0,0 +1,42 @@
+package com.openisle.controller;
+
+import com.openisle.model.PasswordStrength;
+import com.openisle.model.PublishMode;
+import com.openisle.service.PasswordValidator;
+import com.openisle.service.PostService;
+import lombok.Data;
+import lombok.RequiredArgsConstructor;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping("/api/admin/config")
+@RequiredArgsConstructor
+public class AdminConfigController {
+    private final PostService postService;
+    private final PasswordValidator passwordValidator;
+
+    @GetMapping
+    public ConfigDto getConfig() {
+        ConfigDto dto = new ConfigDto();
+        dto.setPublishMode(postService.getPublishMode());
+        dto.setPasswordStrength(passwordValidator.getStrength());
+        return dto;
+    }
+
+    @PostMapping
+    public ConfigDto updateConfig(@RequestBody ConfigDto dto) {
+        if (dto.getPublishMode() != null) {
+            postService.setPublishMode(dto.getPublishMode());
+        }
+        if (dto.getPasswordStrength() != null) {
+            passwordValidator.setStrength(dto.getPasswordStrength());
+        }
+        return getConfig();
+    }
+
+    @Data
+    public static class ConfigDto {
+        private PublishMode publishMode;
+        private PasswordStrength passwordStrength;
+    }
+}