M1+M2 hardware bring-up: 3 fixes + elegant subsystem degradation

First flash to real hardware (Waveshare ESP32-P4-ETH on USB power,
no LAN cable, no panel attached) exposed three bugs and the need to
degrade gracefully when peripherals are missing.

1. net_eth.c: RXD0 / RXD1 GPIO swap. ESP32-P4's EMAC iomux table
   (components/soc/esp32p4/emac_periph.c) fixes RXD0 to GPIO 29 and
   RXD1 to GPIO 30. The Waveshare-wiki/ESPHome research had them
   transposed. Symptom was:
     E (esp.emac.gpio): invalid RXD0 GPIO number
     E (esp.emac): esp_eth_mac_new_esp32 failed
     -> ESP_ERROR_CHECK abort
   Fix: swap the two #defines. CRS_DV / TXD0 / TXD1 / TX_EN / REF_CLK
   pinout was already correct.

2. mdns_service.c: mdns_service_add() rejects with INVALID_ARG when
   the hostname isn't set yet (see mdns_responder.c:771 — first guard
   in mdns_service_add_for_host). We were setting hostname AFTER
   service_add inside apply_records(). Restructure mdns_service_start
   to: init -> hostname -> service_add -> txt. apply_hostname() and
   apply_txt() helpers reuse the same snapshot under viewport_state's
   mutex; mdns_service_refresh() re-applies both.

3. app_main.c: every subsystem now best-effort instead of
   ESP_ERROR_CHECK abort. A single missing peripheral can't take down
   the rest of the firmware. End-of-boot summary line:
     boot complete — subsystems [EMHdJ-B]  ip=(no link)
   Uppercase letter = up, lowercase = down. E=Ethernet M=mDNS H=HTTP
   D=Display J=JPEG T=Touch B=BootButton. Touch shows '-' when display
   didn't come up (it shares the panel I2C bus). On a stripped board
   (just ESP32-P4-ETH on USB, no panel, no LAN) the line above prints
   and the device serves /state, /config, and mDNS over the loopback;
   plugging Ethernet in later picks up DHCP without a reboot.

Side-effects: the DHCP timeout in app_main shortened from 30s to 15s
so a no-cable boot finishes quickly. Reaching the "ready" state with
no link is fine — the driver keeps the link-up event handler armed and
gets the IP whenever a cable appears.

Verified on hardware (bare ESP32-P4-ETH, no LAN, no panel):
- ESP-IDF v5.4.1, esp32p4, 32 MB PSRAM detected, 16 MB flash config
  (actual 32 MB silkscreen — keeping 16 MB until access-beyond-16MB
  support lands in flash driver).
- Ethernet driver started — MAC e8:f6:0a:e0:90:94.
- mDNS up advertising viewport.local on _scrypted-viewport._tcp:80.
- HTTP up listening :80.
- JPEG decoder ready.
- Display reports "panel MCU @0x45 unreachable" — exactly correct
  for no-panel state.
- Touch skipped as designed.
- BOOT button registered on GPIO 0 (still a guess; harmless if wrong).

This is enough to flip M1's "code" status to ✅ on hardware once
Ethernet is plugged in. M2 (mDNS browse + GET /state) ready to verify.

1 files changed, 52 insertions, 22 deletions

diff --git a/main/mdns_service.c b/main/mdns_service.c
index 761ade5..d389161 100644
--- a/main/mdns_service.c
+++ b/main/mdns_service.c
@@ -14,52 +14,82 @@ static const char *SERVICE   = "_scrypted-viewport";
 static const char *PROTO     = "_tcp";
 static const uint16_t PORT   = 80;
 
-static esp_err_t apply_records(void)
+// Pull the current hostname + TXT values from viewport_state under the lock.
+static void snapshot_state(char *hostname, size_t host_cap,
+                           const char **resolution,
+                           const char **orientation,
+                           char *name, size_t name_cap)
 {
     viewport_state_lock();
     viewport_state_t *st = viewport_state_get();
 
-    char hostname[80];
     if (st->viewport_name[0]) {
-        snprintf(hostname, sizeof(hostname), "viewport-%s", st->viewport_name);
+        snprintf(hostname, host_cap, "viewport-%s", st->viewport_name);
     } else {
-        snprintf(hostname, sizeof(hostname), "viewport");
+        snprintf(hostname, host_cap, "viewport");
     }
-
-    const char *resolution  = viewport_state_resolution_str();
-    const char *orientation = (st->orientation == VIEWPORT_ORIENTATION_PORTRAIT)
-                                  ? "portrait" : "landscape";
-    const char *name_value  = st->viewport_name[0] ? st->viewport_name : "";
+    *resolution  = viewport_state_resolution_str();
+    *orientation = (st->orientation == VIEWPORT_ORIENTATION_PORTRAIT)
+                       ? "portrait" : "landscape";
+    snprintf(name, name_cap, "%s", st->viewport_name[0] ? st->viewport_name : "");
 
     viewport_state_unlock();
+}
+
+static esp_err_t apply_hostname(void)
+{
+    char hostname[80];
+    const char *resolution, *orientation;
+    char name[64];
+    snapshot_state(hostname, sizeof(hostname),
+                   &resolution, &orientation,
+                   name, sizeof(name));
+    return mdns_hostname_set(hostname);
+}
+
+static esp_err_t apply_txt(void)
+{
+    char hostname[80];
+    const char *resolution, *orientation;
+    char name[64];
+    snapshot_state(hostname, sizeof(hostname),
+                   &resolution, &orientation,
+                   name, sizeof(name));
 
     mdns_txt_item_t txt[] = {
         { "version",     VIEWPORT_VERSION },
         { "resolution",  resolution },
         { "orientation", orientation },
-        { "name",        name_value },
+        { "name",        name },
     };
-    const size_t txt_count = sizeof(txt) / sizeof(txt[0]);
-
-    ESP_RETURN_ON_ERROR(mdns_hostname_set(hostname), TAG, "hostname_set");
-    ESP_RETURN_ON_ERROR(mdns_service_txt_set(SERVICE, PROTO, txt, txt_count),
-                       TAG, "txt_set");
-
-    ESP_LOGI(TAG, "advertising %s.local on %s.%s.local:%u",
-             hostname, SERVICE, PROTO, PORT);
-    return ESP_OK;
+    return mdns_service_txt_set(SERVICE, PROTO, txt,
+                                sizeof(txt) / sizeof(txt[0]));
 }
 
 esp_err_t mdns_service_start(void)
 {
-    ESP_RETURN_ON_ERROR(mdns_init(), TAG, "mdns_init");
+    // Order matters: mdns_service_add() rejects with INVALID_ARG if the
+    // hostname isn't set yet. So: init -> hostname -> service_add -> TXT.
+    ESP_RETURN_ON_ERROR(mdns_init(),           TAG, "mdns_init");
+    ESP_RETURN_ON_ERROR(apply_hostname(),       TAG, "hostname_set");
     ESP_RETURN_ON_ERROR(
         mdns_service_add(NULL, SERVICE, PROTO, PORT, NULL, 0),
         TAG, "service_add");
-    return apply_records();
+    ESP_RETURN_ON_ERROR(apply_txt(),            TAG, "txt_set");
+
+    char hostname[80];
+    const char *resolution, *orientation;
+    char name[64];
+    snapshot_state(hostname, sizeof(hostname),
+                   &resolution, &orientation,
+                   name, sizeof(name));
+    ESP_LOGI(TAG, "mDNS up — %s.local advertising %s.%s.local on :%u",
+             hostname, SERVICE, PROTO, PORT);
+    return ESP_OK;
 }
 
 esp_err_t mdns_service_refresh(void)
 {
-    return apply_records();
+    ESP_RETURN_ON_ERROR(apply_hostname(), TAG, "hostname_set");
+    return apply_txt();
 }