fix(sensors): make CPU temperature single-writer

[zjwhitehead]

Summary

• make ctrlSensorTask the sole runtime owner of ESP32 temperature-sensor reads
• prime the cache during single-threaded startup
• publish the cached float atomically for cross-core monitor readers
• keep getCachedCpuTemperature read-only so monitoring can never reconfigure tsens

This is the remaining useful CPU-temperature portion of #114, rebuilt on current master. The SPI/LVGL portions of #114 are already present on master.

Validation

• ESP32-S3 production target build: PASS
• native unit tests: 60/60 PASS
• native screenshot tests: 34/34 PASS
• cpplint: PASS

Hardware acceptance

• boot with display, BLE, and monitoring enabled and confirm no tsens reconfiguration errors
• confirm CPU temperature is plausible and refreshes approximately once per second
• exercise reboot and OTA paths