fix(lint): resolve ESLint errors for unused variables

- Change unused catch parameter to _error in codex-reviewer.ts
- Remove unused ArtifactFilter import in artifacts/manager.ts
- Change unused error parameter to _error in session/recovery.ts
- Remove unused saveState import in session/manager.test.ts
- Convert unknown error to string in githubops.test.ts template literal

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

src/artifacts/manager.ts

@@ -25,7 +25,6 @@ import type {
   ArtifactType,
   SaveArtifactOptions,
   DownloadUrlOptions,
-  ArtifactFilter,
 } from "./types.js";
 
 /** デフォルトTTL (24時間) */

src/review/codex-reviewer.ts

@@ -323,7 +323,7 @@ function buildCodexCommand(
           }
         },
       };
-    } catch (error) {
+    } catch (_error) {
       // ファイル書き込みエラー時はフォールバック
       console.warn("[CodexReviewer] Failed to write temp file, using inline content");
     }

src/session/manager.test.ts

@@ -4,7 +4,6 @@
 
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import {
-  saveState,
   restoreState,
   getPendingSessions,
   deleteSession,

src/session/recovery.ts

@@ -169,7 +169,7 @@ export async function completeSession(
  * @param sessionId - セッションID
  * @param error - エラー情報
  */
-export async function failSession(sessionId: string, error: Error): Promise<void> {
+export async function failSession(sessionId: string, _error: Error): Promise<void> {
   await updateStatus(sessionId, SessionStatus.ERROR);
 
   // エラー情報を記録

test/integration/githubops.test.ts

@@ -35,7 +35,7 @@ function createTestBranch(branchName: string): void {
   try {
     execSync(`git checkout -b ${branchName}`, { encoding: "utf-8" });
   } catch (error: unknown) {
-    throw new Error(`Failed to create branch: ${error}`);
+    throw new Error(`Failed to create branch: ${String(error)}`);
   }
 }