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/core/class-pgm-autoloader.php

@@ -0,0 +1,69 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Class and interface autoloader for the Peptide GEO Monitor plugin.
+ *
+ * Converts PGM_* class/interface names to file paths under includes/.
+ * Naming conventions:
+ *   PGM_Foo_Bar (class)      → class-pgm-foo-bar.php
+ *   PGM_Foo_Bar (interface)  → interface-pgm-foo-bar.php (tried second)
+ *
+ * Who triggers: Plugin boot (peptide-geo-monitor.php) — called once before
+ *               any PGM_* class or interface is instantiated.
+ * Dependencies: None (pure PHP).
+ *
+ * @package PeptideGeoMonitor
+ */
+class PGM_Autoloader {
+
+	/**
+	 * Register the autoloader with the SPL stack.
+	 *
+	 * @return void
+	 */
+	public static function register(): void {
+		spl_autoload_register( array( static::class, 'load' ) );
+	}
+
+	/**
+	 * Attempt to load a PGM_* class or interface file.
+	 *
+	 * Walks the known include subdirectories in order, trying the class-
+	 * filename first and the interface-filename second.
+	 *
+	 * Side effects: require_once on a matching file.
+	 *
+	 * @param string $class_name Fully-qualified class or interface name.
+	 *
+	 * @return void
+	 */
+	public static function load( string $class_name ): void {
+		if ( 0 !== strpos( $class_name, 'PGM_' ) ) {
+			return;
+		}
+
+		$slug = strtolower( str_replace( '_', '-', $class_name ) );
+
+		$search_dirs = array(
+			PGM_PLUGIN_DIR . 'includes/core/',
+			PGM_PLUGIN_DIR . 'includes/providers/',
+			PGM_PLUGIN_DIR . 'includes/collector/',
+			PGM_PLUGIN_DIR . 'includes/panel/',
+			PGM_PLUGIN_DIR . 'includes/',
+		);
+
+		// Try class file first, then interface file.
+		$candidates = array( 'class-' . $slug . '.php', 'interface-' . $slug . '.php' );
+
+		foreach ( $search_dirs as $dir ) {
+			foreach ( $candidates as $file ) {
+				$path = $dir . $file;
+				if ( file_exists( $path ) ) {
+					require_once $path;
+					return;
+				}
+			}
+		}
+	}
+}