feat: restore NVS runtime config with CLI commands (NVS > build-time priority)

Bring back two-layer configuration: build-time defaults from mimi_secrets.h
with runtime NVS overrides via serial CLI. NVS values take highest priority
so a pre-flashed board can be reconfigured anywhere with just a USB cable.

Restored CLI commands: wifi_set, set_tg_token, set_api_key, set_model,
set_proxy, clear_proxy, set_search_key. Added new commands: config_show
(displays all config with sensitive fields masked), config_reset (clears
all NVS overrides), and help (lists all commands).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main/mimi_config.h

@@ -2,7 +2,7 @@
 
 /* MimiClaw Global Configuration */
 
-/* Build-time secrets (sole configuration method) */
+/* Build-time secrets (highest priority, override NVS) */
 #if __has_include("mimi_secrets.h")
 #include "mimi_secrets.h"
 #endif
@@ -88,3 +88,19 @@
 #define MIMI_CLI_PRIO                3
 #define MIMI_CLI_CORE                0
 
+/* NVS Namespaces */
+#define MIMI_NVS_WIFI                "wifi_config"
+#define MIMI_NVS_TG                  "tg_config"
+#define MIMI_NVS_LLM                 "llm_config"
+#define MIMI_NVS_PROXY               "proxy_config"
+#define MIMI_NVS_SEARCH              "search_config"
+
+/* NVS Keys */
+#define MIMI_NVS_KEY_SSID            "ssid"
+#define MIMI_NVS_KEY_PASS            "password"
+#define MIMI_NVS_KEY_TG_TOKEN        "bot_token"
+#define MIMI_NVS_KEY_API_KEY         "api_key"
+#define MIMI_NVS_KEY_MODEL           "model"
+#define MIMI_NVS_KEY_PROXY_HOST      "host"
+#define MIMI_NVS_KEY_PROXY_PORT      "port"
+