Add free-text api_instructions field to Sites

For custom sites we'll post to via their own API — there's no wired-in
publisher for these, so this is where the site owner documents how to
actually post there (auth, endpoints, payload shape). Shown in the UI
for non-WordPress sites, exposed via the JSON API, and pointed to from
AI_API.md's "any other network/CMS" fallback section so an agent checks
it before improvising.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

resources/views/livewire/sites/index.blade.php

@@ -34,6 +34,8 @@
                                     {{ $revealedId === $site->id ? 'Hide' : 'Show' }}
                                 </button>
                             </div>
+                        @elseif ($site->api_instructions)
+                            <div class="text-xs text-gray-500" title="{{ $site->api_instructions }}">Has API instructions</div>
                         @endif
                     </td>
                     <td class="p-3 text-right space-x-2">
@@ -89,6 +91,13 @@
                         <input type="text" wire:model="wpAppPassword" class="w-full border rounded p-2">
                         @error('wpAppPassword') <span class="text-red-600 text-sm">{{ $message }}</span> @enderror
                     </div>
+                @else
+                    <div>
+                        <label class="block text-sm font-medium">API Instructions (optional)</label>
+                        <p class="text-xs text-gray-500 mb-1">Notes for posting here via this site's own API — auth method, endpoints, payload shape, etc. Read by whoever (agent or you) ends up publishing to it.</p>
+                        <textarea wire:model="apiInstructions" rows="4" class="w-full border rounded p-2"></textarea>
+                        @error('apiInstructions') <span class="text-red-600 text-sm">{{ $message }}</span> @enderror
+                    </div>
                 @endif
 
                 <div class="flex justify-end gap-2">