add Claude instructions

Signed-off-by: Peter Siegmund <developer@mars3142.org>

firmware/CLAUDE.md

@@ -0,0 +1,88 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+ESP32 firmware for a model railway system control unit, targeting ESP32-S3 and ESP32-C6 microcontrollers. Built with ESP-IDF 5.4. Includes a Svelte 5 web UI (`website/`) and a REST/WebSocket/MQTT API.
+
+## Build Commands
+
+```bash
+# Firmware
+idf.py build
+idf.py -p <PORT> flash
+idf.py -p <PORT> flash monitor
+
+# Release build (ESP32-C6 only)
+make release
+# Equivalent: idf.py -B build-release -DSDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig.release" -DIDF_TARGET=esp32c6 fullclean build size
+
+# Web UI
+cd website && npm install && npm run build
+cd website && npm run test
+```
+
+## Architecture
+
+- `main/` — Firmware entry (`app_main()` in `main.cpp`, core app task in `app_task.cpp`)
+- `components/` — ESP-IDF components with isolated business logic:
+  - **bifrost** (`api-server`) — HTTP REST + WebSocket server, mDNS, static file serving
+  - **connectivity-manager** — WiFi, BLE, captive portal / DNS hijacking
+  - **led-manager** — WS2812 strip control, effects, status LED
+  - **message-manager** — Observer/broadcast bus for cross-component events
+  - **persistence-manager** — NVS abstraction with namespace-scoped typed read/write
+  - **mercedes** — Dynamic menu data model (C++ singleton, JSON-driven)
+  - **hermes** — u8g2 display rendering (menu, splash, screensaver)
+  - **heimdall** — Button/action manager with callback registration
+  - **simulator** — Day/night light cycle simulation from CSV schedules
+- `storage/` — Runtime SPIFFS content: `menu.json`, `schema_*.csv`, `www/` (web assets)
+- `website/` — Svelte 5 + Vite + Tailwind web UI
+
+### Multi-target Support
+
+Two targets are supported with distinct pin assignments and `sdkconfig` defaults:
+- `sdkconfig.defaults` — base (shared)
+- `sdkconfig.defaults.esp32s3` — S3 overrides
+- `sdkconfig.defaults.esp32c6` — C6 overrides (includes WiFi enable/antenna GPIO)
+
+Do not assume one target's pins or settings apply to the other.
+
+### Task Structure
+
+FreeRTOS tasks in priority order:
+1. `app_main()` — hardware init, starts `app_task`
+2. `app_task` — main logic on core 1, priority `tskIDLE_PRIORITY + 5`, 8KB stack
+3. `display_update_task` — async I2C display writes
+
+## Conventions
+
+### C/C++ Style
+- Braces on new line in C files; follow existing formatting per file.
+- Each source file has a local `static const char *TAG = "..."` for `ESP_LOGI/W/E`.
+- HTTP handlers must use `set_cors_headers`, `send_json_response`, and `send_error_response` for consistency.
+- Cross-component state changes go through `message_manager_post(...)`, not direct coupling.
+- Persist settings via `persistence_manager` with a dedicated namespace per feature.
+
+### URI Handler Registration Order (api-server)
+1. Specific `/api/...` handlers
+2. Wildcard API handlers
+3. Captive-portal detection handlers
+4. `OPTIONS /api/*`
+5. Static fallback `/*` (last)
+
+WebSocket handling must be initialized before API handler registration.
+
+### Static Asset Serving
+Preserve correct HTTP headers: content-type, CORS, and `Content-Encoding: gzip` when serving `.gz` variants.
+
+## Key Reference Files
+
+- `README-API.md` — full REST API documentation
+- `README-menu.md` — `menu.json` schema
+- `README-captive.md` — captive portal behavior
+- `components/bifrost/src/api_server.c` — server setup and handler registration
+- `components/bifrost/src/api_handlers.c` — REST endpoint implementations
+- `components/message-manager/src/message_manager.c`
+- `components/persistence-manager/src/persistence_manager.c`
+- `partitions.csv` — flash layout (NVS 16KB, APP 2MB, SPIFFS 1.8MB)