Initial implementation of temporal progress page

Seven particle-based progress cards (hour, day, week, month, year, summer, fall)
with work-time mode toggle and bridge days support. Light elegant design with
accumulating particle animation. Express server proxies dagsmart.se API.

PLAN.md

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+# Aftersummer — Design Plan
+
+## Concept
+A single-page web app showing temporal progress across multiple scales, with an optional work-time mode. Elegant, light, particle-based visuals.
+
+## Visual Design
+- Light warm background (#f7f6f2)
+- Particle accumulation: dark particles fill each card as time passes
+- Elegant sans-serif typography (Inter)
+- No raw percentages — contextual labels only ("42m remaining", "3 working days till summer")
+
+## Cards (7 total, stacked to fill viewport)
+| Card    | Normal mode                     | Work mode                              |
+|---------|---------------------------------|----------------------------------------|
+| Hour    | 0–59 min of current hour        | Same — inactive outside work hours     |
+| Day     | 00:00–23:59                     | 08:00–12:00 + 13:00–17:00 (8h)        |
+| Week    | Mon 00:00 – Sun 23:59           | Mon–Fri, work hours only               |
+| Month   | Calendar days                   | Working days in month                  |
+| Year    | Calendar days                   | Working days in year                   |
+| Summer  | Jan 1 → Midsommarafton progress | Working days — special state in summer |
+| Fall    | 1st Mon Aug → Dec 31 progress   | Working days                           |
+
+## Card States
+- **active**: dark particles accumulating
+- **not-work-time**: muted grey particles, greyed label (outside work hours/days)
+- **summer**: warm amber particles at 100% (Midsommarafton → 1st Mon Aug)
+- **off-season**: cool grey-blue particles at 0% (fall card before fall starts)
+
+## Work Rules
+- Hours: 08:00–12:00 + 13:00–17:00 (8 effective hours, lunch excluded)
+- Days: Mon–Fri
+- July: entirely off (covered by summer period)
+- Holidays: from dagsmart.se API
+- Bridge days: optional (separate toggle)
+
+## Summer / Fall Periods
+- **Summer**: Midsommarafton (from API) → first Monday of August
+- **Pre-summer**: Jan 1 → Midsommarafton
+- **Fall**: first Monday of August → Dec 31
+
+## API
+- **Base URL**: `https://api.dagsmart.se`
+- `GET /holidays?year=YEAR&weekends=false` → `[{ date, code, name: {en, sv} }]`
+  - Note: returns holidays that fall on weekends too (e.g. Easter Saturday) — must check weekends separately
+  - Midsommarafton code: `midsummerEve`
+- `GET /bridge-days?year=YEAR` → `[{ date }]` (no code/name)
+- Cached in localStorage per year, refreshed if stale (different year)
+- Proxied through local server to avoid CORS
+
+## UI Controls
+- **Work time** toggle: switches all cards to work-mode calculations
+- **Bridge days** toggle: visible only when work mode is on; treats bridge days as non-work
+
+## Stack
+- Vanilla JS (ES modules), no framework, no build step
+- Single `public/index.html` + `public/style.css` + `public/app.js`
+- Node.js + Express server: serves static files + proxies API calls
+- `npm start` to run