feat: add device performance check and model compatibility recommendations

[IchenDEV]

Summary

• Device capability detection: New DeviceCapability module reads Apple Silicon chip name, unified memory (RAM), GPU core count, and available disk space via sysctl, IOKit, and FileManager
• Model compatibility checking: Each LLM model in the catalog now carries hardware requirements (min/recommended RAM, disk space). Models are flagged as "compatible", "marginal" (may be slow), or "incompatible" (too large for this Mac)
• UI enhancements: Settings → Models now shows a "This Mac" device info panel with chip, RAM, GPU, and disk at a glance. Model rows display compatibility badges (orange "May Be Slow" / red "Too Large"), and download confirmations include hardware warnings
• Website update: New "Hardware" section on the product page with model-to-hardware mapping table, updated FAQ with hardware guidance, and updated structured data

Test plan

• Verify DeviceCapability.current reports correct chip name, RAM, GPU cores, and disk space
• Check that models exceeding device RAM show "Too Large" badge (e.g. Llama 4 Scout on 8 GB Mac)
• Check that models near the RAM limit show "May Be Slow" badge
• Confirm download confirmation dialog includes compatibility warning for incompatible models
• Verify device info panel renders correctly in Settings → Models
• Test both English and Chinese localizations
• Review docs/index.html hardware section renders correctly

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