Add QArt Tuner: QR code art generator with interactive web UI

Single-file Go tool implementing the QArt technique (Russ Cox, 2012)
using only the public rsc.io/qr API. Generates QR codes whose data
modules form a recognizable image by exploiting error correction
freedom via GF(2) Gaussian elimination.

Includes a web UI with live-updating sliders for version, mask,
rotation, dx/dy offset, and scale. Keyboard shortcuts for rapid
iteration. Also works as a CLI for batch generation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/reference/tools/qart-tuner.md

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+---
+title: QArt Tuner
+modified: 2026-03-27
+tags:
+  - reference
+  - tools
+  - utils
+---
+
+# QArt Tuner
+
+Generates QR codes whose data modules form a recognizable image, using the [QArt technique](https://research.swtch.com/qart) by Russ Cox. Lives in `utils/qart/`.
+
+## Quick Reference
+
+| Item | Value |
+|------|-------|
+| **Source** | `utils/qart/main.go` |
+| **Language** | Go (managed via mise) |
+| **Dependency** | [rsc.io/qr](https://github.com/rsc/qr) (BSD 3-clause) |
+| **Launch web UI** | `QART_IMAGE=photo.png mise run serve` (from `utils/qart/`) |
+| **CLI** | `mise x go -- go run . -url URL -image IMG -out out.png` |
+
+## How It Works
+
+QR error correction (Reed-Solomon coding) allows some data and check bits to be freely chosen. The tool:
+
+1. Builds a QR code plan for the given URL and version
+2. Converts the source photo to a grayscale brightness grid at QR module resolution
+3. For each ECC block, models the data/check bit relationships as a matrix over GF(2)
+4. Uses Gaussian elimination to find which bits can be independently assigned
+5. Assigns bits to match the target image brightness, prioritizing high-contrast areas
+
+The result is a valid, scannable QR code whose black/white modules approximate the source image.
+
+## Web UI
+
+The interactive tuner (`-serve` flag) provides sliders for all parameters with live preview.
+
+**Keyboard shortcuts:** arrow keys (dx/dy offset), `[`/`]` (mask), `-`/`=` (version), `r` (rotate).
+
+## Parameters
+
+| Parameter | Range | Effect |
+|-----------|-------|--------|
+| **version** | 1-8 | QR density — higher = more modules = finer detail |
+| **mask** | 0-7 | QR mask pattern — dramatically affects which pixels are controllable |
+| **dx/dy** | -15 to 15 | Shifts image relative to QR structure (avoids alignment dot on eyes) |
+| **rotation** | 0-3 | Quarter turns |
+| **scale** | 1-16 | Output pixels per QR module |
+| **dither** | on/off | Floyd-Steinberg dithering |
+
+## Credits
+
+- **Technique:** [Russ Cox](https://swtch.com/~rsc/), [QArt Codes](https://research.swtch.com/qart) (2012)
+- **QR library:** [rsc.io/qr](https://github.com/rsc/qr) — QR layout, encoding, GF(256) arithmetic
+- **Implementation:** Claude Code (Opus 4.6) with direction from Erich Blume
+
+## Related
+
+- [[mise-tasks]] — Task runner for BlumeOps operations