Security: Deleted content exposure + revision history IDOR via sequential IDs

## Summary

Two information disclosure issues allow access to deleted/pending content:

### 1. Deleted Answer Content via GET /answer/api/v1/answer/info (Low-Medium)

\`AnswerService.Get()\` calls \`answerRepo.GetByID()\` which fetches answers by raw ID with no \`status != deleted\` filter. Deleted answers are returned with full content to unauthenticated callers.

**Secure comparison:** \`SearchList\` correctly filters: \`session.Where("status != ?", entity.AnswerStatusDeleted)\`

### 2. Revision History IDOR via GET /answer/api/v1/activity/timeline/detail (Medium)

\`GetObjectTimelineDetail\` fetches revision content by sequential integer ID (\`autoincr BIGINT\`). No check for whether the associated question/answer is deleted or pending. Any authenticated user can enumerate \`revision_id=1,2,3...\` to read full content of deleted/pending questions and answers.

**Secure comparison:** \`GetRevisionList\` correctly checks \`objInfo.IsDeleted()\` before showing history. \`GetQuestion\` blocks access to deleted/pending content.

### Impact

- Bypasses content moderation (admin-deleted content remains accessible)
- Reveals pending-review content before publication
- Sequential revision IDs make enumeration trivial

## Discovery

Found through automated security research comparing content visibility controls across endpoints.

影響を受ける2つのエンドポイントについて、まず AnswerService.Get と GetObjectTimelineDetail から始め、そのアクセスチェックを SearchList、GetRevisionList、GetQuestion と比較します。削除済みおよび保留中の質問、回答、リビジョンがどのように読み込まれるかを追跡します。未認証ユーザーに削除済みの回答が公開されず、認証済みユーザーにも削除済みまたは保留中のリビジョンの内容が公開されなくなり、許可されたコンテンツには引き続きアクセスできれば完了です。

索引モデルが issue の本文から書いたものです。