feat: relay hardening — restore build, add tests, negentropy adapter

Restores build broken by eeb9d2d (cvm-relay-stability removed deps):
- CMakeLists.txt: restore display.c, font.c, local_relay.c, relay_selector.c, sync_manager.c, axs15231b, qrcode, wisp_relay
- tollgate_main.c: restore display.h, local_relay.h, relay_selector.h, sync_manager.h includes and display calls
- cvm_server.c: kept master's keepalive/timeout/ping-pong fixes

New test infrastructure:
- test-local-relay, test-relay-nip11, test-cvm-roundtrip, test-cvm-mcp, test-cross-board make targets
- test-cvm-roundtrip.mjs: MCP get_config + get_balance via public relay
- test-cross-board.mjs: cross-board payment test
- test-cvm-mcp-relay.mjs: kept from master

New unit tests (35 tests):
- test_display.c: 22 tests for escape_wifi_field
- test_negentropy_adapter.c: 13 tests for negentropy adapter

New modules:
- negentropy_adapter.c/h: NIP-77 adapter skeleton

Docs:
- AGENTS.md: display module docs, new test commands
- RELAY_HARDENING_PLAN.md: hardening checklist
- RELAY_HARDENING_MERGE.md: merge plan and checklist

Cleanup:
- Removed CHECKLIST-CVM-RELAY.md, PLAN-SQUASH-MERGE.md (stale planning docs)
- Removed components/esp-miner submodule

Host unit tests: 63/63 pass

1 files changed, 27 insertions, 0 deletions

diff --git a/main/negentropy_adapter.h b/main/negentropy_adapter.h
new file mode 100644
index 0000000..1e8c0a8
--- /dev/null
+++ b/main/negentropy_adapter.h
@@ -0,0 +1,27 @@
+#ifndef NEGENTROPY_ADAPTER_H
+#define NEGENTROPY_ADAPTER_H
+
+#include "esp_err.h"
+#include <stdint.h>
+#include <stddef.h>
+
+typedef struct {
+    uint64_t created_at;
+    uint8_t id[32];
+} negentropy_item_t;
+
+typedef struct negentropy_adapter negentropy_adapter_t;
+
+negentropy_adapter_t *negentropy_adapter_from_storage(void *storage_engine);
+
+esp_err_t negentropy_adapter_get_items(negentropy_adapter_t *adapter,
+                                       negentropy_item_t **items,
+                                       size_t *count);
+
+esp_err_t negentropy_adapter_insert_item(negentropy_adapter_t *adapter,
+                                          uint64_t created_at,
+                                          const uint8_t *id);
+
+void negentropy_adapter_destroy(negentropy_adapter_t *adapter);
+
+#endif