Add DC Guardian kit documentation

[fskeung]

Summary

Added complete documentation for DC Guardian kit - a data center monitoring solution.

Changes

• Created kits/dc-guardian/README.md with:
  • Bill of Materials (BOM) with purchase links
  • Wiring diagram with pin connections
  • Assembly instructions
  • PicClaw configuration
  • Cost breakdown
  • ROI calculation
  • Testing and troubleshooting

Bounty Claim

• Issue: docs: create BOM and wiring guide for data center monitoring kit #1
• Task: Create BOM and wiring guide for data center monitoring kit

English Terms Learned

• Bill of Materials (BOM) - 物料清单
• Wiring diagram - 接线图
• Assembly instructions - 组装说明
• Cost breakdown - 成本分析
• ROI (Return on Investment) - 投资回报率

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Note

Low Risk
Low risk: this PR only adds documentation and does not change runtime code paths or configuration used by the system.

Overview
Adds documentation for the new DC Guardian monitoring kit in kits/dc-guardian/README.md, including a BOM with purchase links, wiring/pin mapping, assembly steps, and a sample PicClaw skill.yaml (sensors, thresholds, and notification actions).

Also includes cost/ROI tables plus basic testing commands and troubleshooting guidance.

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