docs: plant seed SEED-002 visualization modes

.planning/seeds/SEED-002-visualization-modes.md

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+---
+id: SEED-002
+status: dormant
+planted: 2026-04-08
+planted_during: v1.0 milestone completion
+trigger_when: v1.1 or next milestone
+scope: medium
+---
+
+# SEED-002: Switchable visualization modes (year/week/day/combined)
+
+## Why This Matters
+
+The current year-view heatmap shows broad patterns but hides finer-grained detail. A week-mode (day-of-week aggregation) reveals which weekdays are busiest. A day-mode (time-of-day heatmap) shows when during the day work happens. A combined day/hour matrix gives the full picture. Together, these modes turn the heatmap from a single view into a flexible time-analysis tool.
+
+## When to Surface
+
+**Trigger:** v1.1 or next milestone
+
+This seed should be presented during `/gsd-new-milestone` when the milestone
+scope matches any of these conditions:
+- Next milestone after v1.0
+- Milestone includes visualization improvements or display modes
+- Milestone includes the INTR-02 requirement (toggle between display modes)
+
+## Scope Estimate
+
+**Medium** — Each mode is a distinct d3 layout (week grid, hour grid, combined matrix) plus a mode switcher UI element. Likely 1-2 phases: one for the mode switcher + week-mode, one for day-mode + combined.
+
+## Breadcrumbs
+
+Related code and decisions found in the current codebase:
+
+- `assets/src/heatmap.ts` — current year-view rendering with `buildGrid()`, `renderHeatmap()`, week interval logic
+- `assets/src/types.ts` — `DayEntry` type (has `date`, `totalHours`, `entryCount`) — day-mode would need hour-level data
+- `src/Service/HeatmapService.php` — `getAggregatedData()` groups by DATE — hour-mode would need GROUP BY HOUR
+- `src/Controller/HeatmapController.php` — API endpoint would need a `mode` query param
+- REQUIREMENTS.md (archived) — INTR-02: "Toggle between hours-per-day and entry-count display modes" (v2 deferred)
+
+## Notes
+
+- The existing `renderHeatmap()` function could be refactored to accept a layout strategy
+- Week-mode and day-mode need different backend aggregation queries
+- Consider whether the mode switcher is tabs, a dropdown, or segmented control (Tabler has all three)
+- The combined day/hour matrix is the most complex — may warrant its own phase