feat: add tollgate_core ESP-IDF component with mining support

Cherry-picked component skeleton from feature/tollgate-core-component arch branch,
extended with mining payment and stratum proxy modules.

Component structure:
  components/tollgate_core/
    include/tollgate_core.h       — public API (core + mining)
    include/tollgate_platform.h   — platform interface (config + mining callbacks)
    src/tollgate_core.c           — orchestrator (init, payment, tick, owner)
    src/tollgate_core_cashu.c/h   — Cashu V3 token decode/verify
    src/tollgate_core_dns.c/h     — per-client DNS hijack/forward
    src/tollgate_core_firewall.c/h — per-client NAT filter
    src/tollgate_core_session.c/h — session lifecycle
    src/tollgate_core_mining.c/h  — hashprice, share validation, client stats
    src/tollgate_core_stratum_proxy.c/h — local SV1 TCP server
    idf_component.yml             — IDF Component Manager metadata

Also fixes nucula_src save_proofs visibility (public).

idf.py build: PASS
make test-unit: PASS (19 suites, 344+ assertions)

1 files changed, 6 insertions, 0 deletions

diff --git a/components/tollgate_core/idf_component.yml b/components/tollgate_core/idf_component.yml
new file mode 100644
index 0000000..112aa18
--- /dev/null
+++ b/components/tollgate_core/idf_component.yml
@@ -0,0 +1,6 @@
+version: "1.0.0"
+description: TollGate core component — Cashu payment processing, per-client DNS/firewall, session management for paid WiFi hotspots
+url: https://github.com/nicoulaj/esp32-tollgate
+dependencies:
+  idf:
+    version: ">=5.4.0"