http_api: bump httpd stack to 8 KiB — POST /config was overflowing

POST /config has ~2.4 KiB of stack locals (2 KiB body buffer + the
scrypted URL + viewport name + cJSON parser frames) which overran the
default 4 KiB httpd task stack and tripped the stack-protect canary
mid-handler. The request body was applied to RAM + NVS, but the
handler crashed before sending the response, so curl saw a connection
reset and the device rebooted into "Stack protection fault".

M4 + M6 ✅ verified 2026-06-14 after the bump:
  - POST /config full / partial → 204; survives reboot via NVS
  - 5 validation failure modes → 400
  - POST /state wake/sleep → 204; idempotent repeats → 204
  - POST /frame while asleep → 409 with expected body
  - idle timer fires after idle_timeout_ms; 0 correctly disables

0 files changed, 0 insertions, 0 deletions