betrieb: Logs je Thema in Tagesdateien (billing, ki, monitoring, market); Doku: Duplicate-Content-Decision durch Anhang 2 abgelöst

- config/logging.php: Themen-Channels billing, ki, monitoring, market als
  daily-Dateien mit gemeinsamer Aufbewahrung (LOG_DAILY_DAYS), Stack-Default
  auf daily; Channel `testing` für die Suite.
- Fachliche Log-Aufrufe in Billing, KI-Jobs, OperationalAlert und
  Kursdaten auf Log::channel() umgestellt.
- phpunit.xml + TestCase: Suite schreibt ausschließlich nach
  testing-YYYY-MM-DD.log; LogChannelsTest sichert die Konfiguration.
- docs/weiteres: Decision-Update Duplicate-Content entfernt (überholt durch
  Roadmap-Anhang 2), Decision-Update Verlinkung & Backlinks als Referenz
  wieder abgelegt, README-Index nachgezogen.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/Feature/LogChannelsTest.php

@@ -0,0 +1,69 @@
+<?php
+
+use App\Services\Web\MarketDataService;
+use App\Support\OperationalAlert;
+use Illuminate\Support\Facades\Http;
+use Illuminate\Support\Facades\Log;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Log-Aufteilung: je Thema eine Tagesdatei, das allgemeine Log bleibt für
+ * Exceptions und Unzugeordnetes. Die Suite selbst schreibt nur nach
+ * testing-*.log (phpunit.xml + TestCase::setUp).
+ */
+test('every topic channel writes its own daily file with the shared retention', function (string $channel, string $file) {
+    // TestCase biegt die Themen-Channels für die Suite um — hier zählt die
+    // ausgelieferte Konfiguration aus config/logging.php.
+    $config = require base_path('config/logging.php');
+
+    expect($config['channels'][$channel])
+        ->toMatchArray([
+            'driver' => 'daily',
+            'path' => storage_path("logs/{$file}.log"),
+            'days' => 14,
+        ]);
+})->with([
+    'billing' => ['billing', 'billing'],
+    'ki' => ['ki', 'ki'],
+    'monitoring' => ['monitoring', 'monitoring'],
+    'market' => ['market', 'market'],
+    'admin_slow' => ['admin_slow', 'admin-slow'],
+]);
+
+test('the default stack rotates daily instead of growing one single file', function () {
+    $config = require base_path('config/logging.php');
+
+    expect($config['channels']['stack']['channels'])->toBe(['daily'])
+        ->and($config['channels']['daily']['path'])->toBe(storage_path('logs/laravel.log'));
+});
+
+test('the test suite logs into the dedicated testing channel only', function () {
+    expect(config('logging.default'))->toBe('testing')
+        ->and(config('logging.channels.testing.path'))->toBe(storage_path('logs/testing.log'));
+
+    foreach (['billing', 'ki', 'monitoring', 'market'] as $channel) {
+        expect(config("logging.channels.{$channel}.path"))->toBe(storage_path('logs/testing.log'));
+    }
+});
+
+test('operational alerts go to the monitoring channel', function () {
+    config()->set('monitoring.alerts.enabled', false);
+    $monitoringLog = Mockery::spy(LoggerInterface::class);
+    Log::shouldReceive('channel')->once()->with('monitoring')->andReturn($monitoringLog);
+
+    OperationalAlert::send('Bounce-Postfach konnte nicht gelesen werden');
+
+    $monitoringLog->shouldHaveReceived('critical')
+        ->withArgs(fn (string $message): bool => str_contains($message, 'Bounce-Postfach'))
+        ->once();
+});
+
+test('market data failures go to the market channel', function () {
+    Http::fake(['*' => Http::response('', 500)]);
+    $marketLog = Mockery::spy(LoggerInterface::class);
+    Log::shouldReceive('channel')->with('market')->andReturn($marketLog);
+
+    app(MarketDataService::class)->refresh();
+
+    $marketLog->shouldHaveReceived('warning')->atLeast()->once();
+});