M4: NVS-backed /config with partial updates + validation

nvs_config.{h,c} — persist the runtime config (viewport, scrypted,
idle_timeout_ms, orientation, brightness) under a single NVS namespace.
nvs_config_load() applies persisted values over the in-RAM defaults on
boot and flips state from UNCONFIGURED to ASLEEP once both name and
Scrypted URL are present. nvs_config_save() commits the whole record
atomically.

http_api.c — add GET /config and POST /config:
  - GET serializes viewport_state to the spec's JSON shape, with null
    for unset string fields and defaults filled in for the rest.
  - POST is partial: each field is optional; only present fields are
    validated and applied. Validation runs on a staged copy and errors
    short-circuit with 400 + reason before any state mutation, so a
    rejected request leaves the device untouched.
  - Validation rules: viewport non-empty <64 chars; scrypted starts with
    http:// and <256 chars; idle_timeout_ms 0 or >=5000; orientation in
    {portrait,landscape}; brightness 0..100.
  - Side-effects fire after the lock + save: brightness change pushes
    PWM to the panel MCU; viewport/orientation change reapplies mDNS
    hostname + TXT.
  - 204 on success; 400 with a single-line reason on validation error.

app_main calls nvs_config_load() right after viewport_state_init(), so
mdns_service_start() and display_init() see the persisted hostname,
orientation, and brightness from the first packet/PWM.

Build clean against ESP-IDF 5.4 (binary ~620 KB).

TESTING.md M3 now documents the Hosyond jumper wiring (5V/GND/SDA=GPIO7/
SCL=GPIO8 from board to panel header; DSI FPC carries only the high-
speed lanes). M4 entry expands the validation matrix and side-effects
to verify.

1 files changed, 4 insertions, 3 deletions

diff --git a/main/app_main.c b/main/app_main.c
index c3c12c0..316f702 100644
--- a/main/app_main.c
+++ b/main/app_main.c
@@ -2,6 +2,7 @@
 #include "http_api.h"
 #include "mdns_service.h"
 #include "net_eth.h"
+#include "nvs_config.h"
 #include "viewport_state.h"
 
 #include "esp_event.h"
@@ -18,6 +19,7 @@ void app_main(void)
     ESP_ERROR_CHECK(esp_event_loop_create_default());
 
     viewport_state_init();
+    nvs_config_load();  // apply persisted config over defaults (best-effort)
     ESP_LOGI(TAG, "Scrypted Viewport boot (v%s)", VIEWPORT_VERSION);
 
     ESP_ERROR_CHECK(net_eth_init());
@@ -30,8 +32,8 @@ void app_main(void)
     ESP_ERROR_CHECK(mdns_service_start());
     ESP_ERROR_CHECK(http_api_start());
 
-    // Display is best-effort during bring-up: a missing/miswired panel must
-    // not kill networking + /state. M3 acceptance: show a test pattern.
+    // Display is best-effort — a missing/miswired panel must not kill
+    // networking + /state. M3 acceptance: show a test pattern.
     if (display_init() == ESP_OK) {
         display_test_pattern();
         ESP_LOGI(TAG, "display up — test pattern on screen");
@@ -39,7 +41,6 @@ void app_main(void)
         ESP_LOGW(TAG, "display init failed — continuing without panel");
     }
 
-    // TODO M4: /config persistence (NVS) + GET /config + POST /config
     // TODO M5: /frame JPEG decode -> framebuffer
     // TODO M6: POST /state + idle timer
     // TODO M7: Capacitive touch -> outbound /state POST