feat: AI usage logging (AiLogger, ai_logs table, admin view)

- AiLogger.php: new service, inserts into ai_logs on every AI call
- ai_logs table: added to migrate.php (provider, model, call_type, tokens, duration_ms)
- AiBot: logs chat, media_response, nlu calls with timing and token counts
- MediaTranscriber: logs whisper, geminiAudio, openaiVision, geminiVision, claudeVision
- /admin/ai-logs: paginated table with provider/company filter
- Layout.php: added IA Logs nav link
- index.php: require AiLogger before AiBot; added GET /admin/ai-logs route

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

services/AiLogger.php

@@ -0,0 +1,40 @@
+<?php
+declare(strict_types=1);
+
+class AiLogger
+{
+    public static function log(
+        ?int    $companyId,
+        string  $provider,
+        string  $model,
+        string  $callType,
+        string  $inputPreview,
+        string  $outputPreview,
+        int     $durationMs,
+        string  $phone      = '',
+        ?int    $tokensIn   = null,
+        ?int    $tokensOut  = null
+    ): void {
+        try {
+            db()->prepare("
+                INSERT INTO ai_logs
+                    (company_id, phone_number, provider, model, call_type,
+                     input_preview, output_preview, tokens_in, tokens_out, duration_ms)
+                VALUES (?,?,?,?,?,?,?,?,?,?)
+            ")->execute([
+                $companyId ?: null,
+                $phone !== '' ? $phone : null,
+                $provider,
+                $model,
+                $callType,
+                mb_substr($inputPreview,  0, 500),
+                mb_substr($outputPreview, 0, 500),
+                $tokensIn,
+                $tokensOut,
+                $durationMs,
+            ]);
+        } catch (\Throwable) {
+            // Never break the bot for a log failure
+        }
+    }
+}