Refactor: Split cost reporting into separate class

Extract read-only reporting methods from PRAutoBlogger_Cost_Tracker into a new
PRAutoBlogger_Cost_Reporter class. This reduces Cost_Tracker from 313 to 206
lines and Reporter to 141 lines, both under the 300-line cap.

Changed files:
- Create includes/core/class-cost-reporter.php with reporting methods:
  * get_monthly_spend(): float
  * get_daily_spend(int $days = 30): array
  * get_spend_by_stage(string $start_date, string $end_date): array
  * get_budget_utilization(): float

- Update includes/core/class-cost-tracker.php:
  * Remove reporting methods
  * Update is_budget_exceeded() and would_exceed_budget() to use Cost_Reporter
  * Keep get_current_run_cost() (tracks current pipeline run only)
  * Add @see cross-reference to Cost_Reporter

- Update templates and admin classes to instantiate Cost_Reporter:
  * templates/admin/metrics-page.php
  * templates/admin/settings-page.php
  * includes/admin/class-admin-notices.php
  * includes/admin/class-dashboard-widget.php

- Split tests/unit/Core/CostTrackerTest.php:
  * Create tests/unit/Core/CostReporterTest.php for reporter methods
  * Keep run ID and budget enforcement tests in CostTrackerTest

Autoloader automatically discovers PRAutoBlogger_Cost_Reporter class.

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

tests/unit/Core/CostReporterTest.php

@@ -0,0 +1,93 @@
+<?php
+/**
+ * Tests for PRAutoBlogger_Cost_Reporter.
+ *
+ * Validates monthly spend, daily spend trends, spend-by-stage breakdowns,
+ * and budget utilization reporting methods.
+ *
+ * @package PRAutoBlogger\Tests\Core
+ */
+
+namespace PRAutoBlogger\Tests\Core;
+
+use PRAutoBlogger\Tests\BaseTestCase;
+use Brain\Monkey\Functions;
+
+class CostReporterTest extends BaseTestCase {
+
+    /**
+     * @var \PHPUnit\Framework\MockObject\MockObject Mock $wpdb instance.
+     */
+    private $wpdb;
+
+    protected function setUp(): void {
+        parent::setUp();
+
+        $this->wpdb = $this->create_mock_wpdb();
+        $GLOBALS['wpdb'] = $this->wpdb;
+
+        // CostReporter methods call get_option for budget settings.
+        $this->stub_get_option( [
+            'prautoblogger_monthly_budget_usd' => '50.00',
+        ] );
+
+        // Stub current_time used in date-based queries.
+        $this->stub_current_time( '2026-04-12 10:00:00' );
+    }
+
+    protected function tearDown(): void {
+        unset( $GLOBALS['wpdb'] );
+        parent::tearDown();
+    }
+
+    /**
+     * Test get_monthly_spend returns float.
+     */
+    public function test_get_monthly_spend_returns_float(): void {
+        $this->wpdb->method( 'prepare' )->willReturn( 'prepared' );
+        $this->wpdb->method( 'get_var' )->willReturn( '10.50' );
+
+        $reporter = new \PRAutoBlogger_Cost_Reporter();
+        $spend = $reporter->get_monthly_spend();
+
+        $this->assertIsFloat( $spend );
+        $this->assertGreaterThanOrEqual( 0.0, $spend );
+    }
+
+    /**
+     * Test get_daily_spend returns array.
+     */
+    public function test_get_daily_spend_returns_array(): void {
+        $this->wpdb->method( 'prepare' )->willReturn( 'prepared' );
+        $this->wpdb->method( 'get_results' )->willReturn( [] );
+
+        $reporter = new \PRAutoBlogger_Cost_Reporter();
+        $daily = $reporter->get_daily_spend( 30 );
+
+        $this->assertIsArray( $daily );
+    }
+
+    /**
+     * Test get_spend_by_stage returns array.
+     */
+    public function test_get_spend_by_stage_returns_array(): void {
+        $this->wpdb->method( 'prepare' )->willReturn( 'prepared' );
+        $this->wpdb->method( 'get_results' )->willReturn( [] );
+
+        $reporter = new \PRAutoBlogger_Cost_Reporter();
+        $spend = $reporter->get_spend_by_stage( '2026-04-01', '2026-04-30' );
+
+        $this->assertIsArray( $spend );
+    }
+
+    /**
+     * Test get_budget_utilization returns float between 0 and 100+.
+     */
+    public function test_get_budget_utilization_returns_float(): void {
+        $reporter = new \PRAutoBlogger_Cost_Reporter();
+        $utilization = $reporter->get_budget_utilization();
+
+        $this->assertIsFloat( $utilization );
+        $this->assertGreaterThanOrEqual( 0.0, $utilization );
+    }
+}