fix(firmware,server): watchdog crash + no detection from edge vitals (#321, #323)

* fix(firmware,server): watchdog crash on busy LANs + no detection from edge vitals (#321, #323)

**Firmware (#321):** edge_dsp task now batch-limits frame processing to 4
frames before a 10ms yield. On corporate LANs with high CSI frame rates,
the previous 1-tick-per-frame yield wasn't enough to prevent IDLE1
starvation and task watchdog triggers.

**Sensing server (#323):** When ESP32 runs the edge DSP pipeline (Tier 2+),
it sends vitals packets (magic 0xC5110002) instead of raw CSI frames.
Previously, the server broadcast these as raw edge_vitals but never
generated a sensing_update, so the UI showed "connected" but "0 persons".
Now synthesizes a full sensing_update from vitals data including
classification, person count, and pose generation.

Closes #321
Closes #323

Co-Authored-By: claude-flow <ruv@ruv.net>

* fix(firmware): address review findings — idle busy-spin and observability

- Fix pdMS_TO_TICKS(5)==0 at 100Hz causing busy-spin in idle path (use
  vTaskDelay(1) instead)
- Post-batch yield now 2 ticks (20ms) for genuinely longer pause
- Add s_ring_drops counter to ring_push for diagnosing frame drops
- Expose drop count in periodic vitals log line

Co-Authored-By: claude-flow <ruv@ruv.net>

* fix(server): set breathing_band_power for skeleton animation from vitals

When presence is detected via edge vitals, set breathing_band_power to
0.5 so the UI's torso breathing animation works. Previously hardcoded
to 0.0 which made the skeleton appear static even when breathing rate
was being reported.

Co-Authored-By: claude-flow <ruv@ruv.net>

firmware/esp32-csi-node/main/edge_processing.c

@@ -41,12 +41,14 @@ static const char *TAG = "edge_proc";
  * ====================================================================== */
 
 static edge_ring_buf_t s_ring;
+static uint32_t s_ring_drops;  /* Frames dropped due to full ring buffer. */
 
 static inline bool ring_push(const uint8_t *iq, uint16_t len,
                              int8_t rssi, uint8_t channel)
 {
     uint32_t next = (s_ring.head + 1) % EDGE_RING_SLOTS;
     if (next == s_ring.tail) {
+        s_ring_drops++;
         return false;  /* Full — drop frame. */
     }
 
@@ -788,12 +790,13 @@ static void process_frame(const edge_ring_slot_t *slot)
 
         if ((s_frame_count % 200) == 0) {
             ESP_LOGI(TAG, "Vitals: br=%.1f hr=%.1f motion=%.4f pres=%s "
-                     "fall=%s persons=%u frames=%lu",
+                     "fall=%s persons=%u frames=%lu drops=%lu",
                      s_breathing_bpm, s_heartrate_bpm, s_motion_energy,
                      s_presence_detected ? "YES" : "no",
                      s_fall_detected ? "YES" : "no",
                      (unsigned)s_latest_pkt.n_persons,
-                     (unsigned long)s_frame_count);
+                     (unsigned long)s_frame_count,
+                     (unsigned long)s_ring_drops);
         }
     }
 
@@ -831,18 +834,32 @@ static void edge_task(void *arg)
 
     edge_ring_slot_t slot;
 
+    /* Maximum frames to process before a longer yield.  On busy LANs
+     * (corporate networks, many APs), the ring buffer fills continuously.
+     * Without a batch limit the task processes frames back-to-back with
+     * only 1-tick yields, which on high frame rates can still starve
+     * IDLE1 enough to trip the 5-second task watchdog.  See #266, #321. */
+    const uint8_t BATCH_LIMIT = 4;
+
     while (1) {
-        if (ring_pop(&slot)) {
+        uint8_t processed = 0;
+
+        while (processed < BATCH_LIMIT && ring_pop(&slot)) {
             process_frame(&slot);
-            /* Yield after every frame to feed the Core 1 watchdog.
-             * process_frame() is CPU-intensive (biquad filters, Welford stats,
-             * BPM estimation, multi-person vitals) and can take several ms.
-             * Without this yield, edge_dsp at priority 5 starves IDLE1 at
-             * priority 0, triggering the task watchdog. See issue #266. */
+            processed++;
+            /* 1-tick yield between frames within a batch. */
             vTaskDelay(1);
+        }
+
+        if (processed > 0) {
+            /* Post-batch yield: 2 ticks (~20 ms at 100 Hz) so IDLE1 can
+             * run and feed the Core 1 watchdog even under sustained load.
+             * This is intentionally longer than the 1-tick inter-frame yield. */
+            vTaskDelay(2);
         } else {
-            /* No frames available — yield briefly. */
-            vTaskDelay(pdMS_TO_TICKS(1));
+            /* No frames available — sleep one full tick.
+             * NOTE: pdMS_TO_TICKS(5) == 0 at 100 Hz, which would busy-spin. */
+            vTaskDelay(1);
         }
     }
 }