Wi-Fi Tools: scan logging to CSV, plus sort and filter

- lib/wifi (host-tested): scan_log (CSV field quoting, header/row, a
  once-per-interval throttle) and network_list_view (sort by signal /
  channel / name, filter open-only / hide-hidden / strong-only)
- ScanEntry moved to lib/wifi so both are testable on the PC
- Wi-Fi Tools networks view: s sort, o/h/w filters, l toggles logging
  to /wifi/scans/<date>.csv (header + one row per AP per logged scan,
  throttled 30 s, needs the clock for timestamps); foreground-only
- Wi-Fi scan logs replace probe-request logs as a clean-up category
- Serial: cat <path>, and key <char> injects a character

Verified on the device: CSV written with header, timestamps, BSSID,
channel, RSSI, security and SSID; hidden networks marked.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

docs/milestones/M1.md

@@ -10,7 +10,7 @@ The "Done when" items below work on the device, against irc.libera.chat over TLS
   - **Wi-Fi Tools is built from ordinary scans only:** networks nearby, channel occupancy and a signal tracker. Monitoring-mode views and captures are deferred (revised Q42). The Monitoring mode stays in the Wi-Fi Service and the IRC pause logic, unused for now.
   - **The frame buffer is 8-bit colour** (Q46), applied as soon as IRC on TLS measured a 51 KB low.
 - **Not done, carried over:**
-  - **Probe-request logs and Wi-Fi captures** are still listed as Storage Clean-up categories, but nothing writes to them yet.
+  - **Wi-Fi scan logs** (a CSV of the access points each scan sees) can be recorded from Wi-Fi Tools; monitoring-mode captures remain deferred.
   - **IRC has no input history** (up-arrow recall). Each Buffer keeps only 50 lines in RAM; the full history is in the Logs.
 - **Measured on the device:**
   - With Wi-Fi and IRC on TLS: about 92 KB free heap, about 77–81 KB at the lowest. The floor was 40 KB.