feat: add non-streaming LLM API, tool registry, and web_search tool

Replace SSE streaming with non-streaming JSON for Anthropic API.
Add llm_chat_tools() returning structured llm_response_t with text
and tool_use blocks. Implement tool registry with dispatch-by-name
and web_search tool via Brave Search API (direct + proxy support).

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

main/tools/tool_registry.c

@@ -0,0 +1,92 @@
+#include "tool_registry.h"
+#include "tools/tool_web_search.h"
+
+#include <string.h>
+#include "esp_log.h"
+#include "cJSON.h"
+
+static const char *TAG = "tools";
+
+#define MAX_TOOLS 8
+
+static mimi_tool_t s_tools[MAX_TOOLS];
+static int s_tool_count = 0;
+static char *s_tools_json = NULL;  /* cached JSON array string */
+
+static void register_tool(const mimi_tool_t *tool)
+{
+    if (s_tool_count >= MAX_TOOLS) {
+        ESP_LOGE(TAG, "Tool registry full");
+        return;
+    }
+    s_tools[s_tool_count++] = *tool;
+    ESP_LOGI(TAG, "Registered tool: %s", tool->name);
+}
+
+static void build_tools_json(void)
+{
+    cJSON *arr = cJSON_CreateArray();
+
+    for (int i = 0; i < s_tool_count; i++) {
+        cJSON *tool = cJSON_CreateObject();
+        cJSON_AddStringToObject(tool, "name", s_tools[i].name);
+        cJSON_AddStringToObject(tool, "description", s_tools[i].description);
+
+        cJSON *schema = cJSON_Parse(s_tools[i].input_schema_json);
+        if (schema) {
+            cJSON_AddItemToObject(tool, "input_schema", schema);
+        }
+
+        cJSON_AddItemToArray(arr, tool);
+    }
+
+    free(s_tools_json);
+    s_tools_json = cJSON_PrintUnformatted(arr);
+    cJSON_Delete(arr);
+
+    ESP_LOGI(TAG, "Tools JSON built (%d tools)", s_tool_count);
+}
+
+esp_err_t tool_registry_init(void)
+{
+    s_tool_count = 0;
+
+    /* Register web_search */
+    tool_web_search_init();
+
+    mimi_tool_t ws = {
+        .name = "web_search",
+        .description = "Search the web for current information. Use this when you need up-to-date facts, news, weather, or anything beyond your training data.",
+        .input_schema_json =
+            "{\"type\":\"object\","
+            "\"properties\":{\"query\":{\"type\":\"string\",\"description\":\"The search query\"}},"
+            "\"required\":[\"query\"]}",
+        .execute = tool_web_search_execute,
+    };
+    register_tool(&ws);
+
+    build_tools_json();
+
+    ESP_LOGI(TAG, "Tool registry initialized");
+    return ESP_OK;
+}
+
+const char *tool_registry_get_tools_json(void)
+{
+    return s_tools_json;
+}
+
+esp_err_t tool_registry_execute(const char *name, const char *input_json,
+                                char *output, size_t output_size)
+{
+    for (int i = 0; i < s_tool_count; i++) {
+        if (strcmp(s_tools[i].name, name) == 0) {
+            ESP_LOGI(TAG, "Executing tool: %s", name);
+            return s_tools[i].execute(input_json, output, output_size);
+        }
+    }
+
+    ESP_LOGW(TAG, "Unknown tool: %s", name);
+    snprintf(output, output_size, "Error: unknown tool '%s'", name);
+    return ESP_ERR_NOT_FOUND;
+}