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, 49 insertions, 0 deletions

diff --git a/main/viewport_state.h b/main/viewport_state.h
new file mode 100644
index 0000000..b580ff7
--- /dev/null
+++ b/main/viewport_state.h
@@ -0,0 +1,49 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#define VIEWPORT_VERSION       "0.1.0"
+#define VIEWPORT_PANEL_WIDTH   800
+#define VIEWPORT_PANEL_HEIGHT  480
+
+typedef enum {
+    VIEWPORT_ORIENTATION_PORTRAIT = 0,  // effective: 480x800
+    VIEWPORT_ORIENTATION_LANDSCAPE,     // effective: 800x480
+} viewport_orientation_t;
+
+typedef enum {
+    VIEWPORT_STATE_UNCONFIGURED = 0,
+    VIEWPORT_STATE_AWAKE,
+    VIEWPORT_STATE_ASLEEP,
+} viewport_run_state_t;
+
+// Read-mostly snapshot of device state used by /state. Counters are
+// updated under a mutex by the modules that own them.
+typedef struct {
+    char     viewport_name[64];         // empty before /config
+    char     scrypted_url[256];         // empty before /config
+    bool     configured;
+    viewport_run_state_t state;
+
+    uint8_t  brightness;                // 0–100, default 80
+    uint32_t idle_timeout_ms;           // 0 = disabled, else >= 5000, default 60000
+    viewport_orientation_t orientation; // default portrait
+
+    uint64_t boot_us;                   // esp_timer_get_time() at boot
+    int64_t  last_frame_us;             // -1 if no frame received yet
+
+    uint64_t frames_received;
+    uint64_t decode_errors;
+    uint64_t state_post_failures;
+} viewport_state_t;
+
+void viewport_state_init(void);
+viewport_state_t *viewport_state_get(void);
+void viewport_state_lock(void);
+void viewport_state_unlock(void);
+
+// Returns the effective resolution string ("480x800" or "800x480") based
+// on the current orientation. Caller-owned static storage; safe to read
+// without the lock (atomic snapshot).
+const char *viewport_state_resolution_str(void);