docs: plant seed SEED-001 native entity pickers

.planning/seeds/SEED-001-native-entity-pickers.md

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+---
+id: SEED-001
+title: Replace basic dropdown with Kimai's native TomSelect entity pickers
+planted: 2026-04-08
+trigger: next milestone focused on UX polish, or when activity filtering gets added
+status: planted
+---
+
+# SEED-001: Native Entity Pickers
+
+## Why
+
+Phase 4 shipped a plain `<select>` dropdown for project filtering. Kimai has a production-ready cascading picker system (Customer → Project → Activity) built on TomSelect with autocomplete, search, color-coded options, and consistent styling. Using it would:
+
+- Enable activity filtering (currently descoped)
+- Add customer-level filtering (cascade: customer → project)
+- Match Kimai's native UX patterns
+- Get autocomplete/search for free
+
+## What
+
+Replace the `<select class="form-select">` in `heatmap.ts` with Kimai's `KimaiFormSelect.js` + TomSelect integration. Use `data-api-url`, `data-related-select`, and `data-empty-url` attributes to wire up cascading.
+
+## Breadcrumbs
+
+- `dev/kimai/assets/js/forms/KimaiFormSelect.js` — cascading logic (lines 386-447)
+- `dev/kimai/assets/js/forms/KimaiFormTomselectPlugin.js` — base TomSelect wrapper
+- `dev/kimai/src/Form/Type/ProjectType.php` — Symfony form type with `api_data` config
+- `dev/kimai/src/Form/Type/ActivityType.php` — activity picker form type
+- API routes: `get_customers`, `get_projects`, `get_activities`
+- Current implementation: `assets/src/heatmap.ts` init() function, lines 236-276
+
+## Scope Estimate
+
+Medium — needs backend changes (new API endpoint or reuse existing routes) + frontend refactor of the filter section. Tests need updating.