Add comprehensive SPI programmer best practices guide with safety warnings and modern recommendations

[Copilot]

This PR addresses the critical need for safer SPI programming practices by creating comprehensive documentation that prioritizes user safety and recommends modern, reliable programmers over dangerous alternatives.

Problem

The existing flashing guides only mentioned CH341A programmers without proper safety warnings. Many users reported bricked laptops due to:

• Old CH341A programmers outputting dangerous 5V instead of 3.3V
• Lack of guidance on proper safety procedures
• No information about better alternatives like Tigard or CH341A rev 1.6+

Solution

Created a comprehensive SPI Programmer Best Practices guide that:

🔧 Programmer Recommendations (Priority Order)

1. Tigard ($67-89) - Fast, multi-protocol, excellent reliability
2. CH341A rev 1.6+ ($5-15) - Budget option with voltage selector
3. Raspberry Pi Pico ($4-10) - DIY option with good performance
4. CH347 ($5-15) - Newer, safer alternative to old CH341A

⚠️ Critical Safety Features

• Prominent warnings about power disconnection (battery, AC, CMOS)
• Voltage selection guidance (start with 1.8V, try 3.3V)
• Never connect/disconnect while powered warnings
• Visual identification guide for CH341A rev 1.6+ vs dangerous old versions

📊 Community-Tested Data

• Real-world speed benchmarks (Tigard: 21s vs CH341A: 120s for 8MB chip)
• Reliability data from extensive community testing
• Wiring color code reference from successful installations

🛠️ Practical Guidance

• Detailed SPI pin mapping with color-coded wiring table
• Troubleshooting guide for common connection issues
• WSON8 package support with specialized probe recommendations
• Flashrom command examples for different programmers

🔗 Integration

• Updated all existing device guides (x230, T430, T420, T480) with safety warnings
• Added prominent safety notice to main flashing guides index
• Reorganized navigation to prioritize safety information

Visual References

The guide includes community-provided images showing:

• CH341A rev 1.6+ identification features (voltage selector switch)
• Comparison between old dangerous CH341A and new safer versions
• WSON8 probe with alignment guide for surface-mount chips

Links to Recommended Kits

• Novacustom: Pre-assembled CH341A rev 1.6+ kits
• 3mdeb: Complete programmer kits with clips
• Crowd Supply: Tigard for advanced users and developers

This comprehensive guide transforms the flashing experience from potentially dangerous trial-and-error to safe, informed practice based on extensive community testing and feedback.

Fixes #120.

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