docs: Complete v0.1 documentation sprint

- Add build & flash workflow (docs/INSTALL.md)
- Add CSI config reference and firmware comparison (docs/USAGE.md)
- Add quick reference cheatsheet (docs/CHEATSHEET.md)
- Add dependencies.lock to .gitignore (env-specific)
- Update TASKS.md with completed items and build notes
- Verified firmware builds on ESP-IDF v6.1.0 / aarch64

docs/INSTALL.md

@@ -0,0 +1,134 @@
+# Build & Flash Guide
+
+## Prerequisites
+
+| Component | Version | Location |
+|-----------|---------|----------|
+| ESP-IDF | v6.1.0 | `~/esp/esp-idf/` |
+| esp-csi | latest | `~/esp/esp-csi/` (reference only) |
+| Xtensa toolchain | GCC 15.2.0 | `~/.espressif/tools/` |
+| Python | 3.13+ | ESP-IDF venv |
+
+**Note:** No RISC-V toolchain installed. Only ESP32 (Xtensa) targets are supported. For ESP32-C3/C5/C6, run `~/esp/esp-idf/install.sh` with the appropriate target first.
+
+## Setup
+
+### 1. Activate ESP-IDF Environment
+
+```bash
+source ~/esp/esp-idf/export.sh
+```
+
+This must be run in every new shell session. It adds `idf.py` and the toolchain to PATH.
+
+### 2. Set Target Chip
+
+```bash
+cd ~/git/esp32-hacking/get-started/csi_recv_router
+idf.py set-target esp32
+```
+
+### 3. Configure WiFi and UDP Target
+
+```bash
+idf.py menuconfig
+```
+
+Navigate to:
+- **Example Connection Configuration** → Set WiFi SSID and password
+- **CSI UDP Configuration** → Set target IP and port
+
+| Setting | Default | Description |
+|---------|---------|-------------|
+| WiFi SSID | (none) | Your router's SSID |
+| WiFi Password | (none) | Your router's password |
+| UDP Target IP | 192.168.129.11 | Pi's IP address |
+| UDP Target Port | 5500 | Listening port on Pi |
+
+## Build
+
+```bash
+cd ~/git/esp32-hacking/get-started/csi_recv_router
+idf.py build
+```
+
+Build output goes to `build/` (excluded by `.gitignore`). External component `esp_csi_gain_ctrl` is fetched automatically to `managed_components/`.
+
+### ESP-IDF v6.1 Workaround
+
+The `esp_csi_gain_ctrl` component (v0.1.4) only ships prebuilt libraries up to ESP-IDF v6.0. On ESP-IDF v6.1+, the build fails with a missing `.a` file. Fix by symlinking:
+
+```bash
+cd managed_components/espressif__esp_csi_gain_ctrl
+ln -s 6.0 6.1
+```
+
+This is needed after every `idf.py fullclean` or component re-fetch. The v6.0 library is ABI-compatible with v6.1.
+
+## Flash
+
+### Connect ESP32
+
+Plug ESP32-DevKitC into USB. The serial port appears as `/dev/ttyUSB0` or `/dev/ttyACM0`.
+
+```bash
+ls /dev/ttyUSB* /dev/ttyACM*
+```
+
+### Flash Firmware
+
+```bash
+idf.py -p /dev/ttyUSB0 flash
+```
+
+### Monitor Serial Output
+
+```bash
+idf.py -p /dev/ttyUSB0 monitor
+```
+
+Exit monitor with `Ctrl+]`.
+
+### Flash + Monitor (combined)
+
+```bash
+idf.py -p /dev/ttyUSB0 flash monitor
+```
+
+## Deployed Devices
+
+| Name | IP | Location | Notes |
+|------|-----|----------|-------|
+| muddy-storm | 192.168.129.29 | Living Room | |
+| amber-maple | 192.168.129.30 | Office | |
+| hollow-acorn | 192.168.129.31 | Kitchen | |
+
+All devices run `csi_recv_router` firmware, sending CSI data to `192.168.129.11:5500`.
+
+## Building Other Firmware Variants
+
+Same process, different directory:
+
+```bash
+# ESP-NOW receiver (serial output)
+cd ~/git/esp32-hacking/get-started/csi_recv
+idf.py set-target esp32 && idf.py build
+
+# ESP-NOW transmitter
+cd ~/git/esp32-hacking/get-started/csi_send
+idf.py set-target esp32 && idf.py build
+
+# Radar console (presence detection)
+cd ~/git/esp32-hacking/esp-radar/console_test
+idf.py set-target esp32 && idf.py build
+```
+
+## Troubleshooting
+
+| Problem | Solution |
+|---------|----------|
+| `idf.py: command not found` | Run `source ~/esp/esp-idf/export.sh` |
+| `/dev/ttyUSB0` not found | Plug in ESP32, check `dmesg \| tail` |
+| Permission denied on serial | `sudo usermod -aG dialout $USER`, then re-login |
+| Build fails on dependencies | `idf.py reconfigure` to re-fetch components |
+| WiFi not connecting | Check SSID/password in `idf.py menuconfig` |