fix(firmware): fall detection false positives + 4MB flash support (#263, #265)

Issue #263: Default fall_thresh raised from 2.0 to 15.0 rad/s² — normal
walking produces accelerations of 2.5-5.0 which triggered constant false
"Fall Detected" alerts. Added consecutive-frame requirement (3 frames)
and 5-second cooldown debounce to prevent alert storms.

Issue #265: Added partitions_4mb.csv and sdkconfig.defaults.4mb for
ESP32-S3 boards with 4MB flash (e.g. SuperMini). OTA slots are 1.856MB
each, fitting the ~978KB firmware binary with room to spare.

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

firmware/esp32-csi-node/provision.py

@@ -168,7 +168,9 @@ def main():
     parser.add_argument("--edge-tier", type=int, choices=[0, 1, 2],
                         help="Edge processing tier: 0=off, 1=stats, 2=vitals")
     parser.add_argument("--pres-thresh", type=int, help="Presence detection threshold (default: 50)")
-    parser.add_argument("--fall-thresh", type=int, help="Fall detection threshold (default: 500)")
+    parser.add_argument("--fall-thresh", type=int, help="Fall detection threshold in milli-units "
+                        "(value/1000 = rad/s²). Default: 15000 → 15.0 rad/s². "
+                        "Raise to reduce false positives in high-traffic areas.")
     parser.add_argument("--vital-win", type=int, help="Phase history window in frames (default: 300)")
     parser.add_argument("--vital-int", type=int, help="Vitals packet interval in ms (default: 1000)")
     parser.add_argument("--subk-count", type=int, help="Top-K subcarrier count (default: 32)")