Significantly enrich docs page with new sections and content

New sections added (both Chinese and English):
- Installation Media: version-specific media file reference table
- How It Works: 13-step execution flow, log file documentation
- Advanced Usage: step-by-step install, one-click patching,
  multi-instance, VirtualBox environment
- Post-Install Verification: single/standalone/RAC verification
  commands with expected outputs
- Troubleshooting: common errors (deps, ASM disks, SSH trust,
  memory, OPatch) with detailed solutions

Enriched existing sections:
- Standalone ASM: added custom install example with redundancy
- RAC: added prerequisites checklist, production RAC example with
  ARCH diskgroup and patches
- FAQ: expanded from 5 to 10 entries (offline install, multi-instance,
  OS changes, ARM support, uninstall)
- Changelog: added v4.2.0, v4.0.0, v3.5.0, v3.0.0 history
- System Requirements: added network, SELinux, firewall notes

New UI elements:
- Tip (green), Warning (orange), Info (blue) callout boxes
- Media reference table style
- Sidebar reorganized with Install Guide and Other categories

Author: pc-study