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.h

@@ -15,7 +15,7 @@
 namespace roro {
 
 // The GNSS receiver on the Cap LoRa-1262 (see CONTEXT.md and docs/milestones/M2.md): reads its
-// NMEA from the main loop's tick (about 450 bytes/s, so a 1 KB UART buffer covers any stall),
+// NMEA from the main loop's tick (about 450 bytes/s, so a 512-byte UART buffer covers a second),
 // holds the current Fix, and sets the clock from it. Settings → GNSS switches it on and off.
 class GnssService : public Service {
    public: