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

.github/workflows/ci.yml

@@ -0,0 +1,78 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_call:
+
+permissions:
+  contents: read
+
+jobs:
+  # ── PHP Syntax Check ─────────────────────────────────────────────
+  lint-php:
+    name: PHP Lint (${{ matrix.php }})
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php: [ '8.1', '8.2', '8.3' ]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up PHP ${{ matrix.php }}
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+
+      - name: Syntax check all PHP files
+        run: find . -name "*.php" -not -path "./vendor/*" | xargs -n 1 php -l
+
+      - name: Unit tests (lightweight, no PHPUnit)
+        run: |
+          for test in tests/unit/test-*.php; do
+            echo "=== Running $test ==="
+            php "$test"
+          done
+
+  # ── WordPress Coding Standards (PHP CodeSniffer) ──────────────────
+  lint-phpcs:
+    name: WordPress Coding Standards
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.1'
+
+      - name: Install Composer dependencies
+        run: composer install --no-interaction --prefer-dist --no-progress
+
+      - name: Run PHPCS
+        run: composer run lint
+        continue-on-error: true
+
+  # ── 300-line file check ──────────────────────────────────────────
+  file-size:
+    name: 300-line file check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Check no PHP file exceeds 300 lines
+        run: |
+          violations=0
+          while IFS= read -r file; do
+            lines=$(wc -l < "$file")
+            if [ "$lines" -gt 300 ]; then
+              echo "VIOLATION: $file ($lines lines)"
+              violations=$((violations + 1))
+            fi
+          done < <(find . -name "*.php" -not -path "./vendor/*" -not -path "./tests/*")
+          if [ "$violations" -gt 0 ]; then
+            echo "$violations file(s) exceed 300 lines"
+            exit 1
+          fi
+          echo "All PHP files are 300 lines or fewer."