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>

database/migrations/2026_05_03_074845_add_response_body_to_api_logs_table.php

@@ -0,0 +1,34 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Adds response_body so ApiLogger can capture what came back from
+     * an external call when it fails. Populated only when the response
+     * was non-2xx or an exception was thrown — successful responses
+     * stay null to keep the table small.
+     *
+     * Truncated to 65,535 chars (TEXT limit) in code; MEDIUMTEXT gives
+     * us headroom for the rare case of a long Anthropic error payload.
+     */
+    public function up(): void
+    {
+        Schema::table('api_logs', function (Blueprint $table) {
+            $table->mediumText('response_body')
+                ->nullable()
+                ->after('error')
+                ->comment('Response body, populated only on failure. Truncated to ~64KB.');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('api_logs', function (Blueprint $table) {
+            $table->dropColumn('response_body');
+        });
+    }
+};