feat(109): checkbox multiselect filters

Phase 109 complete:
- Add checkbox dropdown enhancement for statistics multi-select filters
- Preserve GET contract for channels[] and status_groups[]
- Update PAUL plan context to read .paul/codebase docs

Co-Authored-By: Codex <noreply@openai.com>

.paul/changelog/2026-04-28.md

@@ -0,0 +1,23 @@
+# 2026-04-28
+
+## Co zrobiono
+
+- [Phase 109, Plan 01] Wdrozono checkbox dropdown multi-select filters na `/statistics/orders`.
+- Zachowano kontrakt GET `channels[]` i `status_groups[]` przez synchronizacje z natywnym `<select multiple>`.
+- Zaktualizowano `paul:plan`, aby korzystala z `.paul/codebase/architecture.md` i `.paul/codebase/db_schema.md`.
+- Zsynchronizowano lokalny PAUL framework z Claude do Codex z adaptacja sciezek `~/.claude` na `~/.codex`.
+
+## Zmienione pliki
+
+- `.paul/PROJECT.md`
+- `.paul/ROADMAP.md`
+- `.paul/STATE.md`
+- `.paul/codebase/architecture.md`
+- `.paul/codebase/tech_changelog.md`
+- `.paul/phases/109-checkbox-multiselect-filters/109-01-PLAN.md`
+- `.paul/phases/109-checkbox-multiselect-filters/109-01-SUMMARY.md`
+- `public/assets/css/app.css`
+- `public/assets/js/modules/checkbox-multiselect.js`
+- `resources/scss/app.scss`
+- `resources/views/layouts/app.php`
+- `resources/views/statistics/orders.php`