M2: HTTP server + mDNS service discovery + shared state

- viewport_state.{h,c}: shared state struct (config, run-state, counters,
  orientation, timestamps) behind a FreeRTOS mutex. Modules update it
  under viewport_state_lock(); GET /state serializes a snapshot.
- http_api.{h,c}: starts esp_http_server on :80, registers GET /state.
  Returns the full JSON shape from the spec (name, version, configured,
  state, uptime_ms, last_frame_ms_ago, frames_received, decode_errors,
  state_post_failures, resolution, ip, free_heap, free_psram).
- mdns_service.{h,c}: mdns_init + advertise _scrypted-viewport._tcp.local
  on :80 with version/resolution/orientation/name TXT records.
  mdns_service_refresh() reapplies hostname + TXT after /config writes
  (called from M4 onward).
- main/CMakeLists.txt: add esp_http_server, esp_timer, json, mdns to
  REQUIRES. espressif/mdns added as managed component via
  main/idf_component.yml.

app_main calls viewport_state_init early so any module can read defaults
before /config arrives.

Also adds TESTING.md tracking per-milestone verification status and an
integration test plan to run after M9 (races, failure modes, longevity,
power cycles, negative protocol, multi-viewport).

M1 promoted to "🟡 builds clean" in TESTING.md; combined HW verification
of M1+M2 will be one flash session. Build verified against ESP-IDF 5.4
for target esp32p4 (binary ~550 KB).

1 files changed, 65 insertions, 0 deletions

diff --git a/main/mdns_service.c b/main/mdns_service.c
new file mode 100644
index 0000000..761ade5
--- /dev/null
+++ b/main/mdns_service.c
@@ -0,0 +1,65 @@
+#include "mdns_service.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include "esp_check.h"
+#include "esp_log.h"
+#include "mdns.h"
+
+#include "viewport_state.h"
+
+static const char *TAG       = "mdns";
+static const char *SERVICE   = "_scrypted-viewport";
+static const char *PROTO     = "_tcp";
+static const uint16_t PORT   = 80;
+
+static esp_err_t apply_records(void)
+{
+    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);
+    } else {
+        snprintf(hostname, sizeof(hostname), "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 : "";
+
+    viewport_state_unlock();
+
+    mdns_txt_item_t txt[] = {
+        { "version",     VIEWPORT_VERSION },
+        { "resolution",  resolution },
+        { "orientation", orientation },
+        { "name",        name_value },
+    };
+    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;
+}
+
+esp_err_t mdns_service_start(void)
+{
+    ESP_RETURN_ON_ERROR(mdns_init(), TAG, "mdns_init");
+    ESP_RETURN_ON_ERROR(
+        mdns_service_add(NULL, SERVICE, PROTO, PORT, NULL, 0),
+        TAG, "service_add");
+    return apply_records();
+}
+
+esp_err_t mdns_service_refresh(void)
+{
+    return apply_records();
+}