feat: peptide-geo-monitor v0.1.0 — AI-visibility dashboard

Add initial plugin implementation per the CTO engineering handoff
(geomonitor/threads/2026-06-ai-visibility-v1/01-cto-eng-handoff.md).

## What
- PGM_Probe_Provider interface + PGM_Probe_Result value object
- PGM_Perplexity_Provider (sonar via OpenRouter/CF AI Gateway)
- PGM_OpenRouter_Provider (GPT-search + Gemini-search, generic parameterised)
- PGM_Gateway_Client: shared HTTP + exponential-backoff retry (mirrors PRAB)
- PGM_Citation_Detector: domain extraction, is_cited(), get_our_position()
- PGM_Cost_Ledger: MTD cost from DB, can_afford() pre-check, hard monthly cap
- PGM_Probe_Runner: peptides×intents×models run, budget abort, in-run cache
- PGM_Table_Manager: pgm_ai_visibility dbDelta, schema-version, drop_table()
- PGM_Config: typed getters, seed_defaults() (12 peptides, 3 intents, 3 models)
- PGM_Cron: weekly pgm_weekly_probe schedule/clear
- PGM_Data_Collector + PGM_Dashboard_Panel interfaces (seam for future panels)
- PGM_Collector_Registry: singleton registry
- PGM_Ai_Visibility_Collector: trendline, standings, MTD cost (score formula)
- PGM_Ai_Visibility_Panel: proxy note, Chart.js trendline, standings table
- PGM_Admin_Page: GEO Monitor menu, Run now POST handler (nonce+capability)
- uninstall.php: DROP TABLE + DELETE pgm_* options + wp_clear_scheduled_hook
- Unit tests (6 files): citation detection, score calc, cost ledger + budget
  abort, provider response parsing (mock HTTP), cron, uninstall purge
- ARCHITECTURE.md, CONVENTIONS.md, CONTEXT.md (score formula), README.md,
  CHANGELOG.md — same-commit per DoD
- CI workflow: PHP lint (8.1/8.2/8.3) + PHPCS + 300-line check

## Security
- Secrets from wp-config constants only; none hardcoded
- manage_options + nonce on every admin action
- Input sanitized; output escaped

Agent-Session: geomonitor v0.1.0

includes/providers/class-pgm-citation-detector.php

@@ -0,0 +1,80 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Detects whether peptiderepo.com appears in a list of source domains.
+ *
+ * Centralises the citation-detection logic so both providers can share it
+ * without duplication.  Also parses raw citation arrays/URLs into a clean
+ * domain list.
+ *
+ * Who triggers: PGM_Perplexity_Provider, PGM_OpenRouter_Provider.
+ * Dependencies: None (pure PHP).
+ *
+ * @see CONTEXT.md — "cited", "our_position", "source_domains".
+ * @package PeptideGeoMonitor
+ */
+class PGM_Citation_Detector {
+
+	/**
+	 * Parse raw citation data from an API response into a clean domain list.
+	 *
+	 * Accepts either a flat array of URL strings or an array of objects with
+	 * a 'url' key (Perplexity style). Unknown shapes are skipped gracefully.
+	 *
+	 * @param array<mixed> $raw_citations Raw citations from the API response.
+	 *
+	 * @return string[] Lowercase domain names (e.g. ['peptiderepo.com', 'examine.com']).
+	 */
+	public function parse_domains( array $raw_citations ): array {
+		$domains = array();
+
+		foreach ( $raw_citations as $item ) {
+			$url = '';
+			if ( is_string( $item ) ) {
+				$url = $item;
+			} elseif ( is_array( $item ) && isset( $item['url'] ) && is_string( $item['url'] ) ) {
+				$url = $item['url'];
+			}
+
+			if ( '' === $url ) {
+				continue;
+			}
+
+			$host = (string) wp_parse_url( $url, PHP_URL_HOST );
+			if ( '' !== $host ) {
+				$domains[] = strtolower( ltrim( $host, 'www.' ) );
+			}
+		}
+
+		return array_values( array_unique( $domains ) );
+	}
+
+	/**
+	 * Detect whether PGM_TARGET_DOMAIN appears in a domain list.
+	 *
+	 * @param string[] $domains Parsed domain list from parse_domains().
+	 *
+	 * @return bool
+	 */
+	public function is_cited( array $domains ): bool {
+		return in_array( PGM_TARGET_DOMAIN, $domains, true );
+	}
+
+	/**
+	 * Find the 1-based position of PGM_TARGET_DOMAIN in a domain list.
+	 *
+	 * Returns null when the target domain is not found.
+	 *
+	 * @param string[] $domains Parsed domain list.
+	 *
+	 * @return int|null
+	 */
+	public function get_our_position( array $domains ): ?int {
+		$pos = array_search( PGM_TARGET_DOMAIN, $domains, true );
+		if ( false === $pos ) {
+			return null;
+		}
+		return (int) $pos + 1; // Convert 0-based index to 1-based position.
+	}
+}