Trim task stacks and buffers by measurement: +15 KB with IRC up

Peak stack use was measured through each task's worst case (an
ECDSA-checked install over Wi-Fi and from SD, get/put, a core dump
fetch, an IRC TLS handshake); stacks are now peak plus about 2 KB: loop
8 -> 6 KB, update 8 -> 5, storage 10 -> 6, irc 8 -> 6. The Debug Build's
console ring goes 6 -> 4 KB, serial TX 2 -> 1 KB, the GNSS UART buffer
1 KB -> 512 B.

On the device, with IRC on TLS: 46 KB free (was 31), an 18 KB low (was
9.4). The re-run of every worst case left at least 1.6 KB of stack free
in each task.

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

src/services/gnss_service.cpp

@@ -32,7 +32,7 @@ void GnssService::start() {
 void GnssService::stop() { close(); }
 
 void GnssService::open(uint32_t nowMs) {
-    Serial1.setRxBufferSize(1024);  // before begin(): over 2 s of NMEA
+    Serial1.setRxBufferSize(512);  // before begin(): over a second of NMEA, read every 50 ms
     Serial1.begin(kBaud, SERIAL_8N1, kRxPin, kTxPin);
     open_ = true;
     active_ = false;  // tick() wakes it or puts it to sleep, per the setting