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, 78 insertions, 0 deletions

diff --git a/main/negentropy_adapter.c b/main/negentropy_adapter.c
new file mode 100644
index 0000000..2939289
--- /dev/null
+++ b/main/negentropy_adapter.c
@@ -0,0 +1,78 @@
+#include "negentropy_adapter.h"
+#include "storage_engine.h"
+#include <stdlib.h>
+#include <string.h>
+#include "esp_log.h"
+
+static const char *TAG = "negentropy_adapter";
+
+struct negentropy_adapter {
+    void *storage;
+    negentropy_item_t *items;
+    size_t count;
+    size_t capacity;
+};
+
+negentropy_adapter_t *negentropy_adapter_from_storage(void *storage_engine)
+{
+    if (!storage_engine) return NULL;
+
+    negentropy_adapter_t *adapter = calloc(1, sizeof(negentropy_adapter_t));
+    if (!adapter) return NULL;
+
+    adapter->storage = storage_engine;
+    adapter->items = NULL;
+    adapter->count = 0;
+    adapter->capacity = 0;
+
+    return adapter;
+}
+
+esp_err_t negentropy_adapter_get_items(negentropy_adapter_t *adapter,
+                                       negentropy_item_t **items,
+                                       size_t *count)
+{
+    if (!adapter || !items || !count) return ESP_ERR_INVALID_ARG;
+
+    if (adapter->items) {
+        free(adapter->items);
+        adapter->items = NULL;
+    }
+    adapter->count = 0;
+    adapter->capacity = 0;
+
+    *items = adapter->items;
+    *count = adapter->count;
+
+    ESP_LOGI(TAG, "Adapter has %zu items", adapter->count);
+    return ESP_OK;
+}
+
+esp_err_t negentropy_adapter_insert_item(negentropy_adapter_t *adapter,
+                                          uint64_t created_at,
+                                          const uint8_t *id)
+{
+    if (!adapter || !id) return ESP_ERR_INVALID_ARG;
+
+    if (adapter->count >= adapter->capacity) {
+        size_t new_cap = adapter->capacity == 0 ? 64 : adapter->capacity * 2;
+        negentropy_item_t *new_items = realloc(adapter->items, new_cap * sizeof(negentropy_item_t));
+        if (!new_items) return ESP_ERR_NO_MEM;
+        adapter->items = new_items;
+        adapter->capacity = new_cap;
+    }
+
+    negentropy_item_t *item = &adapter->items[adapter->count];
+    item->created_at = created_at;
+    memcpy(item->id, id, 32);
+    adapter->count++;
+
+    return ESP_OK;
+}
+
+void negentropy_adapter_destroy(negentropy_adapter_t *adapter)
+{
+    if (!adapter) return;
+    if (adapter->items) free(adapter->items);
+    free(adapter);
+}