fix(heltec_v3): carry V4's confirmed CardKB/joystick pins over to V3

V3 and V4 are pin-compatible per Heltec's docs, and V3's own PIN_GPS_RX/TX/EN
defines are dead code here (ENV_INCLUDE_GPS is never set to 1 in this file),
so there's no reason to keep the blind-guess pins from before. Reuses the
exact CardKB (SDA 3/SCL 4) and joystick (UP 23/DOWN 6/LEFT 47/RIGHT 48/BACK 33)
assignment already confirmed working on real V4 hardware.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

variants/heltec_v3/platformio.ini

@@ -196,7 +196,6 @@ lib_deps =
 ;    boot, so a build with these set still runs fine with nothing plugged in.
 ;    Pair it with Settings > Keyboard > Ext. KB = Compact, which is designed to
 ;    need no joystick at all. The same bus is scanned for environment sensors.
-;    Defaults below: SDA 41, SCL 42.
 ;
 ;  * Wired joystick: four direction pins plus a separate Back button -- the UI
 ;    uses Back unconditionally once UI_HAS_JOYSTICK is set, so it isn't optional.
@@ -211,13 +210,13 @@ lib_deps =
 ;    costs nothing here -- that fallback only feeds KEY_NEXT/KEY_PREV, which the
 ;    solo screens don't act on.
 ;
-; Pins already taken on this board: 8/9/10/11/13/14 (LoRa), 17/18 (OLED I2C),
-; 21 (OLED reset), 0 (PRG), 35 (TX LED), 36 (VEXT), 37 (ADC ctrl), 1 (battery
-; ADC), 26/47/48 (GPS). On top of that the ESP32-S3 reserves 19/20 (USB), 26-32
-; (flash) and 43/44 (UART0), and 0/3/45/46 are strapping pins. That leaves
-; 2, 4-7, 33/34 and 38-42, which is where the defaults below come from -- verify
-; against your own module before soldering. The GPS defines above already look
-; optimistic: on a quad-flash S3, GPIO26 is a flash line.
+; V3 and V4 are pin-compatible per Heltec's own docs, so the defaults below are
+; carried over from the heltec_v4_companion_solo_dual env, where this exact
+; CardKB + joystick combination is confirmed working on real hardware -- still
+; worth checking against your own V3 module before soldering, but not a blind
+; guess like the earlier SDA 41/SCL 42 default was. PIN_GPS_RX=47/TX=48/EN=26
+; above are dead defines on V3 (ENV_INCLUDE_GPS is never set to 1 in this file),
+; so they don't conflict with reusing 47/48 here despite the name.
 [env:Heltec_v3_companion_solo_dual]
 extends = Heltec_lora32_v3
 build_flags =
@@ -234,16 +233,16 @@ build_flags =
   -D UI_SENSORS_PAGE=1
   -D OLED_MISC_FIXED_FONT=1   ; full Latin/Greek/Cyrillic 6x9 font, ~14 KB flash
   ; CardKB on the second I2C bus. Harmless with nothing plugged in.
-  -D ENV_PIN_SDA=41
-  -D ENV_PIN_SCL=42
+  -D ENV_PIN_SDA=3
+  -D ENV_PIN_SCL=4
   ; Wired joystick — comment the block out for a CardKB-only build.
   -D UI_HAS_JOYSTICK=1
   -D UI_HAS_JOYSTICK_UPDOWN=1
-  -D JOYSTICK_UP=4
-  -D JOYSTICK_DOWN=5
-  -D JOYSTICK_LEFT=6
-  -D JOYSTICK_RIGHT=7
-  -D PIN_BACK_BTN=2
+  -D JOYSTICK_UP=23
+  -D JOYSTICK_DOWN=6
+  -D JOYSTICK_LEFT=47
+  -D JOYSTICK_RIGHT=48
+  -D PIN_BACK_BTN=33
 ;  -D PIN_BUZZER=<gpio>
 build_src_filter = ${Heltec_lora32_v3.build_src_filter}
   +<helpers/ui/SSD1306Display.cpp>