feat(phase2b): P2b.1 — Research_Fanout + Research_Judge (curate stage) (#178, v0.28.0)

Additive: parallel research fan-out (curl_multi, quorum, cost-reserve-before-dispatch) + curate judge (dedup/score/run_sources). Live Economy path untouched; Authority activates at P2b.4. QA APPROVE-WITH-P2 685c40b; CI green (PHPUnit verified on VPS runner).

Agent-Session: prab-phase2b-1-merge

includes/providers/interface-research-fanout.php

@@ -0,0 +1,27 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Contract for parallel specialist research fan-out.
+ *
+ * @see core/class-research-fanout.php — Primary implementation.
+ * @see ARCHITECTURE.md                — Phase 2b design.
+ */
+interface PRAutoBlogger_Research_Fanout_Interface {
+
+	/**
+	 * Dispatch N specialist research agents in parallel and collect results.
+	 *
+	 * @param string                $run_id      Pipeline run UUID.
+	 * @param string                $item_key    Article item key for stage scoping.
+	 * @param PRAutoBlogger_Article_Idea $idea   The idea being researched.
+	 * @param PRAutoBlogger_Cost_Tracker $cost_tracker Pipeline cost tracker.
+	 * @return array<int, array{sources: array<int, array{url: string, title: string, excerpt: string, relevance: float}>, agent_role: string}> Results indexed by agent slot (0..N-1). Empty array means quorum not met (run should hold).
+	 */
+	public function dispatch(
+		string $run_id,
+		string $item_key,
+		PRAutoBlogger_Article_Idea $idea,
+		PRAutoBlogger_Cost_Tracker $cost_tracker
+	): array;
+}