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/install/docker.md

@@ -63,7 +63,7 @@ It writes config/workspace on the host:
 - `~/.openclaw/`
 - `~/.openclaw/workspace`
 
-Running on a VPS? See [Hetzner (Docker VPS)](/platforms/hetzner).
+Running on a VPS? See [Hetzner (Docker VPS)](/install/hetzner).
 
 ### Manual flow (compose)