fix(network): stream WiFi API responses to prevent heap exhaustion

[meimeiesther]

Summary

Stream WiFi API responses to prevent heap exhaustion on low-memory devices.

Problem

Under the prior implementation, handleWifiScan and handleWifiList built their full JSON response strings using repeated String += concatenation on the heap. On the ESP32-C3, this can exhaust contiguous heap space needed by the WiFi driver's TX queue, triggering an abort() in lmacRetryTxFrame.

Root cause was confirmed via addr2line decoding of a crash report stack trace.

Changes

src/network/CrossPointWebServer.cpp

• handleWifiScan: stream each network entry individually using sendContent instead of concatenating into a single String; increase buf from 256 → 320 bytes; add overflow guard to skip malformed entries
• handleWifiList: stream each credential individually; use appendEscapedJsonString into a stack buffer; increase escapedSsid from 128 → 256 bytes to safely cover worst-case SSID escaping

Testing

Verified fix resolves the crash on device by reproducing the heap-exhaustion condition (scanning in a WiFi-dense environment under reader load) and confirming clean operation post-patch.

[aBER0724]

Integrated the focused Wi-Fi response streaming fix locally on current master, then strengthened it to use watchdog-safe nonblocking chunk writes and corrected overflow handling so skipped entries cannot produce malformed JSON. Added a focused regression test.

Verification completed before closing:

• Wi-Fi API streaming regression test passed
• WebServer low-memory/watchdog regression test passed
• cppcheck passed with low/medium/high defects enabled
• default and sticky firmware builds succeeded

Integrated by master commits 23f0cf2 and e45d82b. The remaining historical changes on this branch are stale or already superseded, so this PR is now closed as integrated/superseded.