fix(watch13): build with -Os like the other nRF52 solo boards

The Watch13 env still compiled with -Ofast and had run out of flash
after the map, calendar and QR commits. -Os brings it to 70.7%.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

solo/gat562_mesh_watch13/platformio.ini

@@ -13,10 +13,12 @@
 extends = GAT562_Mesh_Watch13
 board_build.ldscript = boards/nrf52840_s140_v6_extrafs.ld
 board_upload.maximum_size = 712704
+; Optimise for size, not speed, as the 30S and the L1 do: the nRF52 Arduino
+; core defaults to -Ofast, which bloats flash by ~200 KB on this solo build.
 ; The offline queue (messages held for the phone app while it's away) at 128,
 ; not the board's 256: on the nRF52 the 256 x 177 B left ~5 KB of heap next to
 ; the on-device UI (which keeps its own history), too little for a sign buffer.
-build_unflags = -D OFFLINE_QUEUE_SIZE=256
+build_unflags = -Ofast -D OFFLINE_QUEUE_SIZE=256
 build_flags =
   ${GAT562_Mesh_Watch13.build_flags}
   -I examples/companion_radio/ui-new
@@ -33,6 +35,7 @@ build_flags =
   ; GPS — re-enable (base undefines it); Serial1 pins 15/16 from variant
   -D ENV_INCLUDE_GPS=1
   -D GPS_BAUD_RATE=9600
+  -Os
   ; Buzzer available on IO3 (pin 21) — uncomment to enable
 ;  -D PIN_BUZZER=21
 ;  -D PIN_VIBRATION=36