docs: add CLAUDE.md with architecture and commands

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+```bash
+# Setup (first time)
+python -m venv .venv
+.venv/bin/pip install -r requirements.txt
+
+# Run dev server
+.venv/bin/python run.py
+
+# Run all tests
+.venv/bin/python -m pytest
+
+# Run a single test file
+.venv/bin/python -m pytest tests/test_time_calc.py -v
+
+# Run a single test
+.venv/bin/python -m pytest tests/test_routes.py::test_create_entry -v
+
+# Production (Gunicorn)
+SECRET_KEY=<secret> ./start.sh
+```
+
+## Architecture
+
+Flask app using the factory pattern (`create_app()` in `app/__init__.py`). The DB is SQLite via SQLAlchemy, stored in `instance/worklog.db`. All vehicle/journey/tax configuration lives in `config.toml` (loaded at startup into `app.config["TOML"]`), not in the database.
+
+**Data flow:**
+- `config.toml` → `app/config_loader.py` → accessed via `get_vehicles()`, `get_journeys()`, `get_bareme(year, cv)`
+- `app/models.py` defines `WorkEntry` (one row per day), `TimeSlot` (N plages horaires per entry), `LeaveBalance` (annual quotas)
+- `app/business/` contains pure functions with no Flask dependencies: `time_calc.py` (minutes/reference), `travel_calc.py` (km, CO2, frais réels), `leave_calc.py` (solde congés/RTT)
+- Routes in `app/routes/` use business functions and config_loader, then render Jinja2 templates
+
+**Key domain rules:**
+- Day types: `WORK | TT | GARDE | ASTREINTE | FORMATION | RTT | CONGE | MALADE | FERIE`
+- Types without journey: `TT, MALADE, CONGE, RTT, FERIE` (see `day_types_without_journey()`)
+- Work reference: 7h45 (465 min) for WORK/TT/FORMATION, 10h (600 min) for GARDE, 0 for absences
+- `total_minutes()` on `WorkEntry` sums `TimeSlot` durations, handles midnight crossing
+- Frais réels: uses `bareme_kilometrique` tranches from config.toml; `km_max = 0` means "no upper limit"
+
+**Frontend:** Tailwind CSS and HTMX loaded from CDN in `base.html`. No build step. JavaScript is inline in templates (only `entry_form.html` has JS for dynamic time slots and journey section visibility).
+
+**Auth:** Handled entirely by HAProxy upstream. The app has no authentication.
+
+**Tests:** `tests/conftest.py` provides `app` and `client` fixtures using an in-memory SQLite DB and a temporary TOML config file. Business logic tests (`test_time_calc.py`, `test_travel_calc.py`) have no Flask dependencies and need no fixtures.