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

uninstall.php

@@ -0,0 +1,34 @@
+<?php
+/**
+ * Peptide GEO Monitor — full data teardown on uninstall.
+ *
+ * Drops the custom pgm_ai_visibility table and deletes every wp_options
+ * row whose name starts with "pgm_". WP-Cron events are already cleared
+ * by PGM_Deactivator on deactivation; this runs after that.
+ *
+ * @see ARCHITECTURE.md — §Uninstall specification.
+ * @see class-pgm-deactivator.php — Clears cron on deactivation.
+ */
+
+if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) {
+	exit;
+}
+
+global $wpdb;
+
+/* ── 1. Drop the custom table ─────────────────────────────────────── */
+
+$table = $wpdb->prefix . 'pgm_ai_visibility';
+// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.SchemaChange, WordPress.DB.PreparedSQL.InterpolatedNotPrepared
+$wpdb->query( "DROP TABLE IF EXISTS {$table}" );
+
+/* ── 2. Delete all pgm_ prefixed options ──────────────────────────── */
+
+// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery
+$wpdb->query(
+	"DELETE FROM {$wpdb->options} WHERE option_name LIKE 'pgm\_%'"
+);
+
+/* ── 3. Clear any remaining scheduled cron events ─────────────────── */
+
+wp_clear_scheduled_hook( 'pgm_weekly_probe' );