Move build system from setuptools to uv, wire uv into CI/CD

Convert both pyproject.toml files to the uv_build backend and turn the
repo into a proper uv workspace (plotstyle moved to src layout, since
uv_build requires the module in its own subdirectory). Dev tooling
moves from an optional-dependencies extra to a dependency-group, and
plotstyle's matplotlib dependency is now its own rather than a
gallery "plotting" extra.

Gitea Actions workflows and the Dockerfile now use astral-sh/setup-uv,
uv sync, uv run, uv build, and uv publish throughout instead of pip,
build, and twine. Also fixes .dockerignore, which was excluding
uv.lock, deploy/, and README.md and would have broken even the
previous Dockerfile's COPY of deploy/entrypoint.sh.

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

plotstyle/README.md

@@ -0,0 +1,40 @@
+# plotstyle
+
+A KIT (Karlsruhe Institute of Technology) corporate-design matplotlib
+styling toolkit — a validated 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) for producing figures that
+look consistent across a thesis and a slide deck.
+
+Requires a local LaTeX toolchain (`latex` + `dvipng`) — `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")
+
+ps.savefig(fig, "plots/measured_signal", formats=("pdf",))
+```
+
+This package is developed as part of the
+[ETPlot](https://git.larsbogner.de/lars/ETPlot) monorepo, where it is paired
+with `gallery`, a static HTML gallery generator that turns directories of
+plot PDFs into a browsable website — `plotstyle` has no code dependency on
+`gallery`, the two only meet on disk via the PDF (and optional
+`metadata.yaml`) files a `plotstyle` script writes out. See that repo's
+`examples/plotstyle_showcase.ipynb` for a fully rendered tour of every
+function, and `plotstyle/CLAUDE.md` for the full API reference.