feat(wallet): lazy keyset loading with exponential backoff + jitter

- Remove eager load_keysets() from init_wallet(), load on first use
- Add ensure_keysets() with binary exponential backoff + random jitter
- Guard all wallet operations (receive, send, melt, swap_all) with ensure_keysets()
- Skip checkstate on TLS failure, let wallet swap verify proofs instead
- Pin HTTP server to core 0 (fixes TLS cert verification in checkstate)
- Rewrite nucula http.c to use manual open/write/read (same as working health probe)
- Disable hardware MPI (CONFIG_MBEDTLS_HARDWARE_MPI=n)
- Add http.h stub for unit tests

Known issue: progressive TLS failure after 2-3 connections (PK verify 0x4290),
wallet receive swap fails. Needs deeper mbedTLS/PSRAM investigation.

1 files changed, 1 insertions, 1 deletions

diff --git a/sdkconfig.defaults b/sdkconfig.defaults
index bed04fe..f67ce67 100644
--- a/sdkconfig.defaults
+++ b/sdkconfig.defaults
@@ -40,6 +40,7 @@ CONFIG_MBEDTLS_CERTIFICATE_BUNDLE=y
 CONFIG_MBEDTLS_DYNAMIC_BUFFER=y
 CONFIG_MBEDTLS_SSL_IN_CONTENT_LEN=4096
 CONFIG_MBEDTLS_SSL_OUT_CONTENT_LEN=4096
+CONFIG_MBEDTLS_HARDWARE_MPI=n
 
 # PSRAM (ESP32-S3 has 8MB)
 CONFIG_SPIRAM=y
@@ -48,4 +49,3 @@ CONFIG_SPIRAM_SPEED_80M=y
 CONFIG_SPIRAM_USE_MALLOC=y
 CONFIG_SPIRAM_MALLOC_ALWAYSINTERNAL=4096
 CONFIG_SPIRAM_MALLOC_RESERVE_INTERNAL=32768
-CONFIG_MBEDTLS_DYNAMIC_BUFFER=y