fix: warn of radio pins that can stop the board booting (#34)

GPIO12 is a strapping pin on the original ESP32: high at reset, it powers
the flash at 1.8 V. A CC1101 can hold GDO2 high at power-up, so a board
with RX on 12 bootloops after a power cut until EN is pressed. It was the
default RX pin.

- RX defaults to GPIO35 on the original ESP32. Saved settings keep their
  pins.
- The log warns each time the radio starts, and the radio settings show a
  warning, while TX, RX or MISO is on a pin whose level at reset can stop
  the chip booting (src/BootPins.h, data-src/js/pins.js).

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

data-src/js/pins.js

@@ -0,0 +1,36 @@
+// The strapping pins whose level at reset can keep each chip from starting
+// the firmware, as src/BootPins.h has them for the log.  A radio that drives
+// one at power-up stops the board booting until EN is pressed (issue #34).
+// The minify step joins this file into index.js; Node loads it on its own for
+// the tests (test/js).
+class BootPins {
+    // A warning for each of the radio config's pins that can stop the board
+    // booting.
+    static radioWarnings(chipModel, config) {
+        const chip = BootPins.CHIPS[chipModel || ''] || {};
+        const warnings = [];
+        for (const [field, name] of BootPins.RADIO) {
+            const pin = config[field];
+            if (field === 'RXPin' && pin === config.TXPin) continue;
+            const effect = chip[pin];
+            if (effect) warnings.push(`${name} is on GPIO-${pin}, a strapping pin: ${effect}.  The radio can hold it there and stop the board booting after a power cut, so move it to another pin.`);
+        }
+        return warnings;
+    }
+}
+// By the chip model the header sends, '' for the original ESP32.
+BootPins.CHIPS = {
+    '': { 0: 'low at reset starts the download mode', 12: 'high at reset powers the flash at 1.8 V' },
+    s2: { 0: 'low at reset starts the download mode', 45: 'high at reset powers the flash at 1.8 V' },
+    s3: { 0: 'low at reset starts the download mode', 45: 'high at reset powers the flash at 1.8 V' },
+    c3: { 9: 'low at reset starts the download mode' },
+    c5: { 28: 'low at reset starts the download mode' },
+    c6: { 9: 'low at reset starts the download mode' },
+    p4: { 35: 'low at reset starts the download mode' },
+    p4es: { 35: 'low at reset starts the download mode' }
+};
+// The radio pins the CC1101 drives at power-up, before it is set up: GDO0
+// puts out a clock, GDO2 CHIP_RDYn, and SO follows CHIP_RDYn while CSN is
+// low.
+BootPins.RADIO = [['TXPin', 'TX'], ['RXPin', 'RX'], ['MISOPin', 'MISO']];
+if (typeof module !== 'undefined' && module.exports) module.exports = { BootPins };