Expand Demobot documentation with operations guide and complete docs navigation

[Copilot]

This PR expands the Demobot docs from a setup+troubleshooting pair into a complete operator-facing documentation set. It improves discoverability and fills the gap between initial setup and day-to-day robot operation.

• Docs IA and entrypoints

  • Updated /README.md and /docs/index.md to present a clear 3-guide structure: Setup, Operations, Troubleshooting.
  • Added a recommended reading flow for new drivers/programmers.

• New operations runbook

  • Added /docs/operations-guide.md covering daily startup, pre-enable checks, enable workflow, live-operation monitoring, shutdown, and escalation triggers.
  • Focused on practical field use and fast safety-oriented decision points.

• Setup guide expansion

  • Extended /docs/setup-guide.md with stronger prerequisites, first-deploy validation checks, explicit failure handoff, and links into troubleshooting/operations.

• Cross-linking and continuity

  • Added contextual links between setup, operations, and troubleshooting so users can move directly from symptom to action.

### Core guides
- [Setup Guide](/docs/setup-guide.md)
- [Operations Guide](/docs/operations-guide.md)
- [Troubleshooting Guide](/docs/troubleshooting.md)