fix(13e6): partition + SPI corruption + bootstrap stay-awake

Three problems surfaced during the first 13.3" end-to-end run:

1) LittleFS IntegerDivideByZero on 200 → write /img.bin. Cause: the
   ~3.5 MB SPIFFS in default_16MB.csv can't fit three 960 KB setup
   screens + a 960 KB cached image (~3.84 MB). Switching to a custom
   partitions_13e6.csv with 24 MB LittleFS on the 32 MB flash.

2) Yellow wash across the panel on long SPI bursts. Cause: SPI DMA
   from a PSRAM-backed scratch buffer hits a cache-coherency window —
   the CPU's writes hadn't reached PSRAM yet when DMA read it. Push
   each half in 8 KB chunks through an internal-SRAM (DMA-coherent)
   scratch, and drop the bus clock to 4 MHz to match the 7.3"
   production speed.

3) Bootstrap window (no image yet) was deep-sleeping for 15 s between
   polls — each cycle a ~5 s ROM-boot + Wi-Fi reconnect, so the user
   waited ~20 s × N retries between scanning the setup QR and seeing
   their first photo land. Now normal_operation_impl returns early
   during bootstrap and main.cpp's normal_operation loops with a
   2 s delay, keeping Wi-Fi up. Once the first image arrives, the
   normal scheduled deep sleep takes over.

   Also fixes a related bug Matt called out: a transient TLS hiccup
   during bootstrap was hitting the 5xx fallback path and painting a
   full yellow fill over the green setup QR, leaving the user with
   no claim path. Criterion is now "does /img.bin exist?" (panel has
   something worth showing with a border) rather than "is currentImgId
   set?", so a fresh device with no cached image preserves the setup
   screen through transient network errors.

Diagnostic prints in the panel driver + [op] start/code lines in
normal_operation_impl that proved invaluable during bringup; leaving
them in for now. Tests updated for the new bootstrap semantics
(deep sleep no longer arms on bootstrap-cycle 204/404/5xx); 43/43
native tests pass, 7.3" production build stays byte-identical.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/panels/waveshare13e6/v1/epd_driver.cpp

@@ -209,6 +209,9 @@ static void ensure_dma_scratch() {
     if (!g_dma_scratch) {
         g_dma_scratch = (uint8_t*)heap_caps_malloc(
             DMA_CHUNK, MALLOC_CAP_INTERNAL | MALLOC_CAP_DMA);
+        Serial.printf("[epd13e6] dma_scratch=%p (free internal=%u)\n",
+                      g_dma_scratch,
+                      (unsigned)heap_caps_get_free_size(MALLOC_CAP_INTERNAL));
     }
 }
 
@@ -235,7 +238,12 @@ static void push_half(int cs_pin, const uint8_t* half_fb, size_t bytes) {
 static void push_full_frame(const uint8_t* fb) {
     constexpr size_t HALF_BYTES = (size_t)HALF_BYTES_ROW * H;
     uint8_t* slice = (uint8_t*)heap_caps_malloc(HALF_BYTES, MALLOC_CAP_SPIRAM);
-    if (!slice) return;
+    if (!slice) {
+        Serial.printf("[epd13e6] push_full_frame: slice alloc FAILED (free PSRAM=%u)\n",
+                      (unsigned)ESP.getFreePsram());
+        return;
+    }
+    Serial.println("[epd13e6] push_full_frame: pushing halves");
 
     for (uint16_t y = 0; y < H; y++) {
         memcpy(slice + (size_t)y * HALF_BYTES_ROW,
@@ -252,6 +260,7 @@ static void push_full_frame(const uint8_t* fb) {
     push_half(PIN_CS_S, slice, HALF_BYTES);
 
     heap_caps_free(slice);
+    Serial.println("[epd13e6] push_full_frame: done");
 }
 
 // ── epd.h surface ──────────────────────────────────────────────────────────────