🔧 chore: enable Renovate fork processing

[ShigureNyako]

Motivation

Enable Renovate to process this fork. Renovate's documentation states that fork opt-in is checked only in onboardingConfigFileName, which defaults to root renovate.json.

Changes

• Move .github/renovate.json5 to root renovate.json and convert it to JSON.
• Preserve extends: ["github>SigureMo/renovate-config"] and add "forkProcessing": "enabled".
• Remove the old configuration so there is only one authoritative Renovate config; root renovate.json takes precedence over .github/renovate.json5.

This PR targets ShigureLab/ci-bypass, not PFCCLab/ci-bypass. No application code or other configuration is changed.

Validation

• Renovate 44.115.10 on Node 24.21.0: renovate-config-validator --strict --no-global renovate.json — passed.
• JSON parsing and assertions for the preserved preset, enabled fork processing, and absence of duplicate configuration — passed.
• git diff --check — passed.

@SigureMo Please review when you have time. Thanks!

[SigureMo]

为啥不能直接在 .github/renovate.json5 加这一行？

[ShigureNyako]

@SigureMo 因为“是否处理 fork”的检查发生在读取常规仓库配置之前；不是 .github/renovate.json5 格式不受支持，而是这个检查不会读取它。

官方文档的 Allowed filenames 明确说这里只支持 onboardingConfigFileName，默认是根目录 renovate.json。对应源码 也只读取这个文件；没有找到文件或其中没有启用 forkProcessing，就直接跳过 fork。因此，在默认配置下，仅在 .github/renovate.json5 加这一行无法让原本被跳过的 fork 开始处理。

所以这里把原有 extends 一起迁到根目录，避免新 renovate.json 优先被读取后丢失共享预设；旧文件随之移除，保持单一配置。如果全局已启用 fork processing（例如 Mend App 的 Selected repositories 模式），则无需靠这项仓库级配置解锁。