feat(heuropt-plot): v0.1.0 — SVG visualization companion crate

Adds heuropt-plot, a tiny SVG-only plotter that takes heuropt
results and emits scatter plots (pareto_front_svg) and line plots
(convergence_svg). No heavy 'plotters' or 'tiny-skia' dep — hand-
rolled SVG so the crate adds <100 KB to a build.

Workspace setup: root Cargo.toml gains [workspace] with members =
['.', 'heuropt-plot']. heuropt-plot has its own version (0.1.0) and
publishes independently against heuropt 0.8+.

Adds examples/visualize.rs that wires it up: NSGA-II on Schaffer
N.1, plain run() (no observer plumbing), final-front SVG written to
disk.

heuropt-plot/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "heuropt-plot"
+version = "0.1.0"
+edition = "2024"
+rust-version = "1.85"
+authors = ["Stephen Waits <steve@waits.net>"]
+description = "Lightweight SVG visualization for heuropt Pareto fronts and convergence traces."
+license = "MIT"
+readme = "README.md"
+repository = "https://github.com/swaits/heuropt"
+homepage = "https://github.com/swaits/heuropt"
+documentation = "https://docs.rs/heuropt-plot"
+keywords = ["optimization", "pareto", "svg", "plotting", "heuropt"]
+categories = ["algorithms", "visualization"]
+
+[dependencies]
+heuropt = { version = "0.8", path = ".." }