The main loop rests between passes (#40)

It made 50,000 passes a second and kept core 1 100 % busy at rest. Keys
are buffered by the keyboard controller, the consoles and the radio have
their own tasks, and no Service ticks more often than every 50 ms, so
the loop now rests 5 ms after a pass with the screen on and 20 ms with
it off; never during a serial file transfer. Safe Mode's loop too.

Screen off: 50 passes a second and core 1 at 1 %; screen on: 167 and
10 %. The chip settles 4 C cooler (34.3 against 38.3). GNSS, Gemini, an
upload, the Sweep and the radio's interrupt all checked at the new pace.
`tasks` shows the loop's passes; Debug Builds: `loop spin on|off`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

README.md

@@ -107,7 +107,7 @@ The LoRa Scanner (docs/milestones/M3.md) listens with the Cap's radio and **neve
 | `irc dump` | Prints IRC status, memory, and the last lines of each Buffer |
 | `wifi status` | Prints Wi-Fi state, network, signal, clock and free heap, then the address, gateway, DNS and NTP servers in use and where each came from |
 | `info` | Firmware, uptime, last start reason, memory, Wi-Fi, the SD card and its write faults since boot, and both app slots with their versions and OTA states |
-| `tasks` | FreeRTOS tasks over the next second: state, priority, lowest free stack, share of a core, and each core's load |
+| `tasks` | FreeRTOS tasks over the next second: state, priority, lowest free stack, share of a core, each core's load, and how many passes the main loop made |
 | `net` | Bytes each network service has read and written since boot |
 | `reboot` / `boot other` | Restart, or restart into the other app slot (a manual Rollback) |
 | `log level <0-5>` | ESP-IDF log level |
@@ -122,6 +122,7 @@ The LoRa Scanner (docs/milestones/M3.md) listens with the Cap's radio and **neve
 | `lora inject <hex> [rssi] [snr]` | Debug Builds: a packet into the Scanner as if received (nothing is sent) |
 | `crash` | The last crash: which firmware, why, task, PC and backtrace (from the core dump in flash) |
 | `coredump erase` | Forgets the core dump |
+| `loop spin on` / `loop spin off` | Debug Builds: make the main loop spin without resting, to compare load and radio noise |
 | `crash abort` / `crash wdt` | Debug Builds: crash on purpose, or hang the main loop until the watchdog fires |
 | `help` | Lists the commands |