Channel width display, wide channel rule, and mobile UI fixes

[tvancott42]

Summary

• Client channel width - Shows the client's negotiated Wi-Fi channel width (20/40/80/160/320 MHz) in the Client Dashboard identity bar, Wi-Fi Optimizer Client Timeline, and Signal History table. Uses the per-client channel_width from stat/sta, not the AP's radio config.
• Wide channel width rule - New Wi-Fi Optimizer rule that flags 6 GHz 320 MHz (unconditional info - narrowing to 160 MHz improves performance and co-channel separation) and 5/6 GHz 160 MHz with weak-signal clients (warning - suggest narrowing to 80 MHz).
• Mobile layout - Hides Ping and Type columns in the speed test table on mobile.
• Speed test time format - Uses time-only format for today's entries, date+time for older.
• Channel Map CSS - Removes extra margin from channel-aps and channel-metrics boxes.

Test plan

• Verify channel width shows correctly in Client Dashboard identity bar (e.g., "Ch 108 - 80 MHz")
• Verify channel width in Wi-Fi Optimizer Client Timeline
• Verify signal history table shows channel width for locally-logged entries only (not historic UniFi entries)
• Run Wi-Fi Optimizer and check wide channel width rule fires for 160+ MHz radios
• Check mobile layout hides Ping/Type columns in speed test table
• Verify Channel Map boxes have no extra margin