docs: restructure Get Started tab and improve onboarding flow (#9950)

* docs: restructure Get Started tab and improve onboarding flow

- Flatten nested Onboarding group into linear First Steps flow
- Add 'What is OpenClaw?' narrative section to landing page
- Split wizard.md into streamlined overview + full reference (reference/wizard.md)
- Move Pairing to Channels > Configuration
- Move Bootstrapping to Agents > Fundamentals
- Move macOS app onboarding to Platforms > macOS companion app
- Move Lore to Help > Community
- Remove duplicate install instructions from openclaw.md
- Mirror navigation changes in zh-CN tabs
- No content deleted — all detail preserved or relocated

* docs: move deployment pages to install/, fix Platforms tab routing, clarify onboarding paths

- Move deployment guides (fly, hetzner, gcp, macos-vm, exe-dev, railway, render,
  northflank) from platforms/ and root to install/
- Add 'Hosting and deployment' group to Install tab
- Slim Gateway & Ops 'Remote access and deployment' down to 'Remote access'
- Swap Platforms tab before Gateway & Ops to fix path-prefix routing
- Move macOS app onboarding into First steps (parallel to CLI wizard)
- Rename sidebar titles to 'Onboarding: CLI' / 'Onboarding: macOS App'
- Add redirects for all moved paths
- Update all internal links (en + zh-CN)
- Fix img tag syntax in onboarding.md

docs/zh-CN/platforms/oracle.md

@@ -307,4 +307,4 @@ tar -czvf openclaw-backup.tar.gz ~/.openclaw ~/.openclaw/workspace
 - [Tailscale 集成](/gateway/tailscale) — 完整的 Tailscale 文档
 - [Gateway 网关配置](/gateway/configuration) — 所有配置选项
 - [DigitalOcean 指南](/platforms/digitalocean) — 如果你想要付费 + 更容易注册
-- [Hetzner 指南](/platforms/hetzner) — 基于 Docker 的替代方案
+- [Hetzner 指南](/install/hetzner) — 基于 Docker 的替代方案