feat: production-ready firmware with BLE memory management, device_id fixes, and docs

- Reduce debug level to 1 (errors only) for production builds
- Replace BLE pause/resume with full deinit/reinit during HTTP uploads (~25KB freed)
- Add 60s boot report delay for fast post-deploy connectivity verification
- Add device_id to BLE batch and heartbeat request bodies
- Correct API host to http:// (plain HTTP, not HTTPS)
- Add HTTP response logging and CV entry/exit serial logging
- Create root README.md with operator setup and architecture overview
- Update design spec: HMAC format, BLE memory approach, request body shapes, reporting intervals

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

firmware/src/reporter.cpp

@@ -30,10 +30,6 @@ static bool post_json(const DeviceConfig& cfg, const char* path, const String& b
 
     HTTPClient http;
     String url = String(REPORTER_API_HOST) + path;
-    // NOTE: Certificate validation is disabled — connection is encrypted but
-    // server identity is not verified. To enable validation, use WiFiClientSecure
-    // with setCACert() before calling http.begin(client, url).
-    // Acceptable for this deployment: devices operate on store WiFi, not public internet.
     http.begin(url);
     http.addHeader("Content-Type", "application/json");
     http.addHeader("X-Device-Id",  cfg.device_id);
@@ -42,6 +38,7 @@ static bool post_json(const DeviceConfig& cfg, const char* path, const String& b
 
     int code = http.POST(body);
     http.end();
+    Serial.printf("[HTTP] POST %s → %d\n", url.c_str(), code);
     return (code == 200);
 }
 
@@ -64,6 +61,7 @@ static String build_camera_batch(const DeviceConfig& cfg,
 static String build_ble_batch(const DeviceConfig& cfg,
                                const std::vector<BLEHourlyRecord>& recs) {
     JsonDocument doc;
+    doc["device_id"]   = cfg.device_id;
     doc["location_id"] = cfg.location_id;
     JsonArray arr = doc["records"].to<JsonArray>();
     for (const auto& r : recs) {
@@ -151,6 +149,7 @@ void reporter_submit_ble(const DeviceConfig& cfg, const BLEHourlyRecord& rec) {
 
 void reporter_heartbeat(const DeviceConfig& cfg, uint32_t uptime_s, int wifi_rssi) {
     JsonDocument doc;
+    doc["device_id"]         = cfg.device_id;
     doc["firmware_version"]  = "1.0.0";
     doc["free_storage_pct"]  = 100;
     doc["wifi_rssi"]         = wifi_rssi;