feat: Implement core frontend application with task management, user selection, and a collapsible sidebar.

Provider/tdd/todo_list.md

@@ -156,7 +156,38 @@ frontend/src/
 └── app.css                      # +sidebar theme tokens
 ```
 
-## 5. Summary
+## 5. Changelog
+
+### 2026-03-07 — API Refactoring & UI Improvements
+
+**Backend Refactoring:**
+- Split monolithic `manage.cpp` and `utils.cpp` into single-responsibility files per endpoint (e.g., `list.cpp`, `add.cpp`, `remove.cpp`)
+- Renamed `seed.cpp` → `store.cpp` in both `api/users/` and `api/tasks/` (better name for the data-store layer)
+- Introduced `store.hpp` forward-declaration headers to resolve cross-domain dependencies (tasks needs `find_user`, users/remove needs `remove_tasks_for_user`)
+- Added `unity.cpp` per domain to simplify `http_server.cpp` includes
+- `.hpp` files contain structs and constants only; all functions live in `.cpp` files
+
+**Frontend OTA Bug Fix:**
+- Fixed `main.cpp` factory-partition check that unconditionally reset `www_part` to 0 on every boot, preventing OTA from ever switching to `www_1`
+- Now only defaults to `www_0` on first boot (NVS key not found); OTA-written values are respected
+
+**Date/Time Picker UX:**
+- Fixed timezone drift bug: `formatDateForInput` used `toISOString()` (UTC) but `datetime-local` inputs use local time, causing ±N hours shift on each edit
+- Split `datetime-local` into separate `date` + `time` inputs with labels
+- Default date/time set to "now" when opening the add task form
+- CSS trick to make Chrome/Edge open the picker on click anywhere in the input (`::-webkit-calendar-picker-indicator` stretched to fill)
+
+**Dashboard Layout:**
+- Moved "Upcoming Tasks" section above the system info grid (content-first, debug tools lower)
+
+**Sidebar:**
+- Auto-collapses on mobile (viewport ≤ 768px) via `window.innerWidth` check at init
+
+**Build Warnings Fixed:**
+- `<button>` inside `<button>` nesting in UserManager → changed user chips to `<div role="button">`
+- `autofocus` a11y warnings suppressed with `<!-- svelte-ignore -->` comments
+
+## 6. Summary
 
 We implement a **temporary in-memory todo list** using **static BSS arrays** on the ESP32 backend, exposed via a **RESTful API** with 8 new endpoints. The frontend gains a **collapsible sidebar** for navigation between the existing Dashboard and a new **Task Manager** view. **Seed data** is populated on every boot for fast development iteration. The architecture is designed to make the eventual migration to **SQLite on SD card** straightforward — the API contracts and frontend components remain unchanged; only the storage layer swaps out.