feat(xce-harness-component): relocate xce_test into standalone harness component

Move xce_test's 15 production sources + headers from src/controller/testsuite/
into a new src/harness/ component with its own meson.build, and strip every
now-dangling controller-side reference (11 controller_unit_test_src entries,
4 standalone test-binary blocks, 11 controller_test.c extern/RUN_TEST lines)
so the controller build is never left broken.

Fixes a broken relative-symlink bridge (xce_test_controller_link) added to
keep two controller-embedded tests (test_test_cli.c, test_xcetest_process_entry.c)
finding the relocated xce_test binary until task 2.1 moves them too.

Discovered and documented in design.md: four controller-domain regression
tests call functions directly from four of xce_test's own files, requiring
controller_unit_test to permanently recompile them from src/harness/ — a
real dependency neither the original discovery nor design audit caught.

controller_unit_test: 1228 Tests 0 Failures 0 Ignored (verified via the
Unity binary's own printed summary line, not just meson's aggregate count).

Task 1.1 of xce-harness-component.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLSNJhNoULvVcUhXEFafQC

src/harness/listfmt_json.c

@@ -0,0 +1,59 @@
+#include "listfmt_json.h"
+
+#include <stdio.h>
+
+cJSON* listfmt_json_begin(void)
+{
+    return cJSON_CreateArray();
+}
+
+void listfmt_json_add_string(cJSON* row, const char* key, const char* val)
+{
+    if (!row || !key)
+        return;
+
+    if (val)
+        cJSON_AddStringToObject(row, key, val);
+    else
+        cJSON_AddNullToObject(row, key);
+}
+
+void listfmt_json_add_number(cJSON* row, const char* key, double val)
+{
+    if (!row || !key)
+        return;
+
+    cJSON_AddNumberToObject(row, key, val);
+}
+
+cJSON* listfmt_json_new_row(cJSON* array)
+{
+    if (!array)
+        return NULL;
+
+    cJSON* row = cJSON_CreateObject();
+    if (!row)
+        return NULL;
+
+    if (!cJSON_AddItemToArray(array, row)) {
+        cJSON_Delete(row);
+        return NULL;
+    }
+
+    return row;
+}
+
+void listfmt_json_finish(cJSON* array)
+{
+    if (!array)
+        return;
+
+    char* text = cJSON_Print(array);
+    if (text) {
+        fputs(text, stdout);
+        fputc('\n', stdout);
+        cJSON_free(text);
+    }
+
+    cJSON_Delete(array);
+}