Use the board detector for displayless boards

[ainyan03]

Requires m5stack/M5GFX#342, which moves the identification of boards without a display into the board detector.

What changes

• The displayless fallback block in _check_boardtype() is removed.
• The board is chosen in this order: the detector's result, an explicit cfg.fallback_board, the detector's candidate (getBoardCandidate()), the remaining ESP32-P4 checks, then a build or package default (_default_fallback_board()).
• cfg.fallback_board now defaults to board_unknown on every target. Setting it still forces the board when the detector cannot confirm one.
• Pin setup follows the chosen board however it was chosen (confirmed, candidate, fallback or default): GPIO46 is restored on the S3 boards that use it, DualKey releases G7 / G8 and has its own pin map, and Capsule sends the I2C STOP and releases its Grove port in its own setup.

Defaults when nothing is confirmed

Chip / package	Default
ESP32 PICO-D4	StampPico
ESP32 PICO-V3	AtomPsram
ESP32 D0WDQ6	TimerCam
ESP32-S3, not LGA56	StampS3 (previously AtomS3Lite)
ESP32-S3 LGA56	StampS3Mini
ESP32-C3	StampC3U
ESP32-C6	NanoC6 / StampC6 by eFuse flash capacity
ESP32-H2	NanoH2
ESP32-C5	StampC5
ESP32-P4	Tab5 (not reached: the remaining P4 GPIO checks always pick a board. #397 moves those checks into the detector and makes this default StampP4 / StampP4X)

BOARD_ID 147 selects DualKey. BOARD_ID 31 / 35 select CoreP4X / Tab5X before the P4 GPIO checks. On ESP32, an Arduino board macro now takes precedence over the package default.

The S3 default changes because AtomS3Lite is now identified by its own pins, so a board that reaches the default is more likely a StampS3.

Tested

On 28 boards together with the M5GFX change (see that PR for the list). Builds: Arduino-ESP32 2.x / 3.x and ESP-IDF 5.x / 6.x for the CI targets.