streaming pivot: raw TCP data plane, drop per-frame HTTP entirely

Replaces the per-frame HTTP POST loop with a single long-lived TCP
connection on port 81. The HTTP control plane (/state, /config,
/frame for snapshot) stays unchanged.

Wire protocol (big-endian, repeating until connection close):
  [4 bytes jpeg_len][4 bytes seq][jpeg_len bytes JPEG]

Why
---
The HTTP path hit a measured floor of ~37ms p50 with intermittent
~230ms p95 spikes that survived every Nagle/keep-alive fix attempt.
Each frame paid: TCP setup (or pool churn), HTTP parsing, body recv,
decode, paint, response write, response ACK. Streaming removes
everything except recv + decode + paint.

Firmware (main/stream_server.[ch], new)
---------------------------------------
- TCP listen on configurable port (81) in its own FreeRTOS task,
  one client at a time (matches the one-stream-per-device model).
- Per accepted socket: TCP_NODELAY on, then loop reading 8-byte
  header → jpeg body → through the existing jpeg_decoder + display
  paths. Same stale-seq guard as the HTTP /frame handler (reset per
  connection so each session starts at seq 1).
- Frames received while asleep are still drained (to stay framed)
  but not painted. The HTTP control-plane POST /state {wake}
  resumes painting on the next frame.
- Every 30 painted frames a structured serial log shows per-stage
  timing + sustained MB/s — replaces the cross-side Server-Timing
  header (no HTTP response to attach it to anymore).

Scrypted side
-------------
- net.createConnection({ host, port: 81, noDelay: true }) opened
  once per stream session. On disconnect/error/close we auto-
  reconnect after 500ms.
- ffmpeg stdout demux writes [header][body] directly to the
  socket. sock.write() returning false sets a backpressured flag
  that drops incoming ffmpeg frames until 'drain' fires — natural
  TCP backpressure handles "firmware can't keep up" without us
  modeling it manually.
- Stripped the entire fetch-based timing infrastructure
  (pushStreamFrame, fetchSamples, parseServerTiming, depth
  histogram, Server-Timing parser). Replaced with one stream-shaped
  log every 10s: fps + MB/s + socket.write p50/p95/max + drop count
  + backpressured flag.
- pushSnapshot (one-shot first-paint) still uses the HTTP /frame
  endpoint — small and infrequent, not worth reworking.
- postJSON still uses node:http for /state and /config.

State machine status flags
--------------------------
Extended boot-time flags array from 6 → 7 slots so the stream
server's bring-up shows up alongside ETH/MDNS/HTTP. Layout is now
E M H S D J T (was E M H D J T).

1 files changed, 6 insertions, 1 deletions

diff --git a/main/app_main.c b/main/app_main.c
index 00a77bb..a6174c8 100644
--- a/main/app_main.c
+++ b/main/app_main.c
@@ -7,6 +7,7 @@
 #include "nvs_config.h"
 #include "state_client.h"
 #include "state_machine.h"
+#include "stream_server.h"
 #include "touch.h"
 #include "viewport_state.h"
 
@@ -52,7 +53,7 @@ void app_main(void)
     // don't get a DHCP lease. mDNS + HTTP advertise / bind anyway and will
     // start serving the moment the link comes up.
     // ------------------------------------------------------------------
-    char flags[7] = { '-','-','-','-','-','-', 0 };  // E M H D J T
+    char flags[8] = { '-','-','-','-','-','-','-', 0 };  // E M H S D J T
     esp_err_t eth_err = net_eth_init();
     mark(eth_err, 'E', &flags[0]);
 
@@ -71,6 +72,10 @@ void app_main(void)
     ESP_ERROR_CHECK(state_client_init());
     mark(mdns_service_start(), 'M', &flags[1]);
     mark(http_api_start(),     'H', &flags[2]);
+    // Data plane: raw TCP on :81 for back-to-back JPEG streaming,
+    // bypassing per-frame HTTP overhead. /frame HTTP stays alive for
+    // the snapshot one-shot and for curl debugging.
+    mark(stream_server_start(81), 'S', &flags[3]);
 
     // ------------------------------------------------------------------
     // Display + I²C-bound peripherals run on their own task. ESP-IDF's