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

tests/unit/test-cron.php

@@ -0,0 +1,64 @@
+<?php
+/**
+ * Tests for PGM_Cron: scheduling, clearing, and registration.
+ *
+ * @package PeptideGeoMonitor
+ */
+
+declare(strict_types=1);
+
+require_once __DIR__ . '/../bootstrap.php';
+
+echo "=== PGM Cron Tests ===\n";
+
+// ── Test: schedule_weekly adds the event ────────────────────────────────
+
+pgm_test_reset();
+pgm_assert( ! PGM_Cron::is_scheduled(), 'schedule_weekly: not scheduled before call' );
+
+PGM_Cron::schedule_weekly();
+pgm_assert( PGM_Cron::is_scheduled(), 'schedule_weekly: event scheduled after call' );
+
+// ── Test: schedule_weekly is idempotent ──────────────────────────────────
+
+PGM_Cron::schedule_weekly(); // Second call should no-op.
+$events = $GLOBALS['pgm_test_state']['cron_events'];
+pgm_assert_equals( 1, count( $events ), 'schedule_weekly: idempotent — second call does not add duplicate' );
+
+// ── Test: clear_schedule removes the event ──────────────────────────────
+
+PGM_Cron::clear_schedule();
+pgm_assert( ! PGM_Cron::is_scheduled(), 'clear_schedule: event removed after clear' );
+
+// ── Test: clear_schedule is safe when nothing scheduled ─────────────────
+
+pgm_test_reset();
+PGM_Cron::clear_schedule(); // Should not throw.
+pgm_assert( ! PGM_Cron::is_scheduled(), 'clear_schedule: safe when nothing scheduled' );
+
+// ── Test: register_hooks registers the cron hook action ─────────────────
+
+pgm_test_reset();
+$cron = new PGM_Cron();
+$cron->register_hooks();
+
+$hooks = array_column( $GLOBALS['pgm_test_state']['actions'], 'hook' );
+pgm_assert( in_array( PGM_CRON_HOOK, $hooks, true ), 'register_hooks: pgm_weekly_probe action registered' );
+
+// ── Test: hook constant is correct string ────────────────────────────────
+
+pgm_assert_equals( 'pgm_weekly_probe', PGM_CRON_HOOK, 'PGM_CRON_HOOK: constant value correct' );
+
+// ── Test: PGM_Activator calls schedule_weekly ────────────────────────────
+
+pgm_test_reset();
+// Seed options so seed_defaults() doesn't fail.
+PGM_Activator::activate();
+pgm_assert( PGM_Cron::is_scheduled(), 'PGM_Activator::activate: weekly cron scheduled after activation' );
+
+// ── Test: PGM_Deactivator calls clear_schedule ───────────────────────────
+
+PGM_Deactivator::deactivate();
+pgm_assert( ! PGM_Cron::is_scheduled(), 'PGM_Deactivator::deactivate: cron cleared after deactivation' );
+
+exit( pgm_test_summary() );