feat(api-logs): persist response body on failed external calls

ApiLogger now stores the upstream response body to
`api_logs.response_body` whenever the call failed (non-2xx response or
a RequestException carrying a response). Successful 2xx responses
remain null so the table stays small on busy services like fuel:poll
and oil:fetch.

Truncated at 64 KB. The column is mediumText so a future cap raise
needs no schema change.

Captures:
- 4xx and 5xx response bodies verbatim
- Body extracted from RequestException via `$e->response->body()`
  when callers use `Http::throw()`

Does not capture:
- ConnectionException (no response existed)
- Generic Throwable from the closure (same reason)

Motivation: the LLM overlay's "skipped — no verified citations" path
left no forensic trail to debug. With this, the next time anything
routed through ApiLogger fails — Anthropic 429s, FRED 5xx, Fuel
Finder errors — the failed body is queryable directly:

    SELECT response_body FROM api_logs
    WHERE service = ? AND status_code >= 400
    ORDER BY id DESC LIMIT 1;

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Unit/ApiLoggerTest.php

@@ -3,6 +3,7 @@
 use App\Models\ApiLog;
 use App\Services\ApiLogger;
 use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Http\Client\RequestException;
 use Illuminate\Support\Facades\Http;
 
 uses(RefreshDatabase::class);
@@ -73,3 +74,48 @@ it('upcases the method', function (): void {
 
     expect(ApiLog::first()->method)->toBe('GET');
 });
+
+it('does NOT store response_body for successful 2xx responses', function (): void {
+    Http::fake(['https://example.com/ok' => Http::response(['large' => str_repeat('x', 5000)])]);
+
+    $this->apiLogger->send('test_service', 'GET', 'https://example.com/ok', fn () => Http::get('https://example.com/ok'));
+
+    expect(ApiLog::first()->response_body)->toBeNull();
+});
+
+it('stores response_body when status code is 4xx', function (): void {
+    Http::fake(['https://example.com/bad' => Http::response('{"error":"bad request"}', 400)]);
+
+    $this->apiLogger->send('test_service', 'GET', 'https://example.com/bad', fn () => Http::get('https://example.com/bad'));
+
+    expect(ApiLog::first()->response_body)->toBe('{"error":"bad request"}');
+});
+
+it('stores response_body when status code is 5xx', function (): void {
+    Http::fake(['https://example.com/boom' => Http::response('Internal Server Error', 500)]);
+
+    $this->apiLogger->send('test_service', 'GET', 'https://example.com/boom', fn () => Http::get('https://example.com/boom'));
+
+    expect(ApiLog::first()->response_body)->toBe('Internal Server Error');
+});
+
+it('truncates response_body at the 64KB cap', function (): void {
+    $hugeBody = str_repeat('A', 80_000);
+    Http::fake(['https://example.com/huge' => Http::response($hugeBody, 502)]);
+
+    $this->apiLogger->send('test_service', 'GET', 'https://example.com/huge', fn () => Http::get('https://example.com/huge'));
+
+    $log = ApiLog::first();
+    expect(strlen($log->response_body))->toBe(65_536);
+});
+
+it('captures response_body when an HTTP RequestException is thrown', function (): void {
+    Http::fake(['https://example.com/throw' => Http::response('upstream details', 502)]);
+
+    expect(fn () => $this->apiLogger->send(
+        'test_service', 'GET', 'https://example.com/throw',
+        fn () => Http::throw()->get('https://example.com/throw')
+    ))->toThrow(RequestException::class);
+
+    expect(ApiLog::first()->response_body)->toBe('upstream details');
+});