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, 46 insertions, 0 deletions

diff --git a/main/viewport_state.c b/main/viewport_state.c
new file mode 100644
index 0000000..9115ce3
--- /dev/null
+++ b/main/viewport_state.c
@@ -0,0 +1,46 @@
+#include "viewport_state.h"
+
+#include <string.h>
+
+#include "esp_timer.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/semphr.h"
+
+static viewport_state_t s_state;
+static SemaphoreHandle_t s_mutex;
+
+void viewport_state_init(void)
+{
+    memset(&s_state, 0, sizeof(s_state));
+    s_state.configured      = false;
+    s_state.state           = VIEWPORT_STATE_UNCONFIGURED;
+    s_state.brightness      = 80;
+    s_state.idle_timeout_ms = 60000;
+    s_state.orientation     = VIEWPORT_ORIENTATION_PORTRAIT;
+    s_state.boot_us         = (uint64_t)esp_timer_get_time();
+    s_state.last_frame_us   = -1;
+
+    s_mutex = xSemaphoreCreateMutex();
+}
+
+viewport_state_t *viewport_state_get(void)
+{
+    return &s_state;
+}
+
+void viewport_state_lock(void)
+{
+    xSemaphoreTake(s_mutex, portMAX_DELAY);
+}
+
+void viewport_state_unlock(void)
+{
+    xSemaphoreGive(s_mutex);
+}
+
+const char *viewport_state_resolution_str(void)
+{
+    return (s_state.orientation == VIEWPORT_ORIENTATION_PORTRAIT)
+               ? "480x800"
+               : "800x480";
+}