M5: POST /frame — hardware JPEG decode + orientation-aware paint

jpeg_decoder.{h,c} wraps esp_driver_jpeg (ESP32-P4 hardware decoder).
- One-time engine + DMA-aligned PSRAM scratch buffer setup (1 MB input,
  768 KB output @ panel native 800x480 RGB565).
- try_lock + unlock so concurrent /frame POSTs get 503 instead of
  queueing, per spec.
- jpeg_decoder_get_info() reports the dimensions; the http handler
  validates them against the effective resolution before painting.

display.h adds display_present_rgb565(src, w, h):
- Landscape: src is 800x480, memcpy 1:1 into the panel framebuffer.
- Portrait: src is 480x800, software rotate 90° CW into the 800x480
  panel framebuffer. (PPA / 2D-DMA hardware rotation is a later
  optimization if portrait latency matters.)

http_api.c adds POST /frame:
- Content-Type must be image/jpeg → else 400.
- Empty body → 400. > 1 MB → 413. Display not initialized → 500.
- jpeg_decoder_try_lock(0) for concurrency: second post returns 503.
- Body streamed into the decoder's input buffer in chunks.
- Decode failure or dimension mismatch → 400 + decode_errors++.
- Paint failure → 500.
- Success → frames_received++, last_frame_us = esp_timer_get_time(),
  204 No Content.

app_main initializes the JPEG decoder after display_init(). Both are
best-effort: failures log a warning and leave the rest of the firmware
running.

CMakeLists.txt: add esp_driver_jpeg to REQUIRES.

Known gap (M6 closes it): /frame currently paints regardless of
wake/sleep state. The 409-when-asleep rule lands with POST /state
in M6.

Build clean against ESP-IDF 5.4 (binary ~640 KB).

TESTING.md M5 expanded with portrait/landscape test commands,
ImageMagick test-image recipes, the full negative matrix (wrong
Content-Type, oversize, wrong dims, concurrent, garbage), and the
M6 dependency note.

1 files changed, 38 insertions, 0 deletions

diff --git a/main/display.c b/main/display.c
index a1a64fd..21e8e5e 100644
--- a/main/display.c
+++ b/main/display.c
@@ -249,6 +249,44 @@ esp_err_t display_fill(uint16_t rgb565)
                                      PANEL_H_ACTIVE, PANEL_V_ACTIVE, fb);
 }
 
+esp_err_t display_present_rgb565(const uint16_t *src,
+                                 uint16_t        src_w,
+                                 uint16_t        src_h)
+{
+    if (!s_up) return ESP_ERR_INVALID_STATE;
+
+    viewport_state_lock();
+    viewport_orientation_t orient = viewport_state_get()->orientation;
+    viewport_state_unlock();
+
+    void *fb = NULL;
+    esp_err_t err = esp_lcd_dpi_panel_get_frame_buffer(s_panel, 1, &fb);
+    if (err != ESP_OK) return err;
+    uint16_t *dst = (uint16_t *)fb;
+
+    if (orient == VIEWPORT_ORIENTATION_LANDSCAPE) {
+        if (src_w != PANEL_H_ACTIVE || src_h != PANEL_V_ACTIVE)
+            return ESP_ERR_INVALID_SIZE;
+        memcpy(dst, src, (size_t)src_w * src_h * sizeof(uint16_t));
+    } else {
+        // Portrait: src is 480x800, rotate 90° CW into the 800x480 panel.
+        // dst dims = src_h x src_w. dst_stride = src_h.
+        // src(x,y) -> dst(x, src_h - 1 - y)
+        if (src_w != PANEL_V_ACTIVE || src_h != PANEL_H_ACTIVE)
+            return ESP_ERR_INVALID_SIZE;
+        const uint16_t dst_stride = src_h;
+        for (uint16_t y = 0; y < src_h; ++y) {
+            const uint16_t *srow = src + (size_t)y * src_w;
+            const uint16_t dst_col = (uint16_t)(src_h - 1 - y);
+            for (uint16_t x = 0; x < src_w; ++x) {
+                dst[(size_t)x * dst_stride + dst_col] = srow[x];
+            }
+        }
+    }
+    return esp_lcd_panel_draw_bitmap(s_panel, 0, 0,
+                                     PANEL_H_ACTIVE, PANEL_V_ACTIVE, fb);
+}
+
 esp_err_t display_test_pattern(void)
 {
     if (!s_up) return ESP_ERR_INVALID_STATE;