Document plotstyle and the Docker deployment switch in CLAUDE.md/README

Root-level docs hadn't caught up with the plotstyle package addition
(KIT styling toolkit, plotting extra, plotstyle/CLAUDE.md pointer) or
the earlier Singularity-to-Docker deployment switch.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -31,6 +31,10 @@
 - TUI: `gallery tui`
 - Config file stored under user `$HOME/.config/gallery`
 
+### Producing Plots (`plotstyle`)
+
+- Companion matplotlib styling toolkit (optional `plotting` extra) for producing figures that look consistent across a thesis and slide deck, ready to drop straight into a gallery source directory — see [Producing Plots with `plotstyle`](#producing-plots-with-plotstyle)
+
 
 ## Installation
 
@@ -54,6 +58,16 @@ gallery --help
 - Python packages are installed automatically by pip (Jinja2, PyYAML, PyMuPDF, Textual, argcomplete, platformdirs)
 - [ImageMagick](https://imagemagick.org/) is **optional** — used as a fallback if `PyMuPDF` is not available
 
+### Optional: `plotstyle` (for producing plots)
+
+```bash
+pip install -e ".[plotting]"
+# or
+uv sync --extra plotting
+```
+
+This only installs `matplotlib` — it's kept out of the core dependencies so a plain gallery install stays lightweight. `plotstyle` also requires a local LaTeX toolchain (`latex` + `dvipng`) to be installed separately; see [Producing Plots with `plotstyle`](#producing-plots-with-plotstyle).
+
 ### Shell Completion (optional)
 
 Install tab-completion for bash/zsh/fish:
@@ -215,6 +229,37 @@ LaTeX formulas are supported in metadata values and rendered with MathJax:
 formula: "$$E = mc^2$$"
 ```
 
+## Producing Plots with `plotstyle`
+
+`plotstyle` is a companion matplotlib styling toolkit shipped in this repo (the `plotstyle/` package) for producing the plots you'll point a gallery source at — a KIT (Karlsruhe Institute of Technology) corporate-design color palette, consistent spines/ticks/gridlines, LaTeX text in a modern sans font, and a few building-block functions (figure titles with a parameters subtitle, a same-size colorbar helper, an outside-axes legend, panel labels). It has no code dependency on `gallery` — the two only meet on disk, through the PDF files (and optional `metadata.yaml`) a `plotstyle` script writes into a directory that `gallery` then scans.
+
+Install it with the `plotting` extra (see [Installation](#installation)) and make sure a LaTeX toolchain (`latex` + `dvipng`) is available locally — `plotstyle` always renders text through real LaTeX, there's no fallback.
+
+```python
+import numpy as np
+import plotstyle as ps
+
+ps.use()  # once, before creating any figure
+
+fig, ax = ps.new_figure(
+    "thesis-single",
+    title="Measured signal",
+    params={"N": 512, "seed": 42},
+)
+x = np.linspace(0, 10, 200)
+ax.plot(x, np.sin(x), label="signal")
+ax.set_xlabel("Time (s)")
+ax.set_ylabel(r"Amplitude $A(t)$")
+ps.style_legend(ax, title="Series")
+
+# Save straight into a gallery source directory:
+ps.savefig(fig, "/path/to/plots/measured_signal", formats=("pdf",))
+```
+
+That PDF (plus an optional `metadata.yaml` next to it, as described above) is exactly what `gallery generate --source /path/to/plots` picks up — `gallery` converts the PDF to a thumbnail PNG itself, so `plotstyle` scripts should stick to `formats=("pdf",)` rather than also producing a PNG.
+
+See `examples/plotstyle_showcase.ipynb` for a fully rendered tour of every function, and `plotstyle/CLAUDE.md` for the full API reference and best practices (aimed at coding agents, but equally useful for humans).
+
 ## Shortcuts
 
 | Icon | Button  | Function                 | Shortcut |