feat(line): add ridgeline as a Line variant (#143)

* feat(line): add ridgeline as a Line variant

One distribution per series, stacked at a fixed pitch on a single shared
amplitude. Ships three static examples (light, dark, full editorial),
the type-line.md spec, and a geometric gate.

verify-ridgeline.py derives the figure's one amplitude and its baseline
pitch from the figure itself, then holds every vertex to both. It also
checks the drawn baseline rules, the shared bin scale, absolute M/L/Z
only, the overlap ceiling, the focus pairing and every label binding.
test-verify-ridgeline.py proves each check in both polarities and pins
the scope treaty with the sibling Line gates.

The contract binds data-bins on a <path>, which no other chart in the
repo declares, so verify-slopegraph and this gate never claim the same
file.

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

* fix(verify-ridgeline): read exponent coordinates as numbers, not commands

parse_d scanned for [A-Za-z] independently of the numbers, so the `e` in a
valid scientific-notation coordinate such as 4.4e2 was counted as a path
command. The explicit-command rule then rejected a correct ridgeline with a
message about command counts.

Tokenise the d attribute left to right with the number branch tried first,
so an exponent is consumed as part of its number. A letter that survives
that branch is a real command and still faces the M/L/Z vocabulary check;
anything else leaves the path unreadable, which stays a finding.

Adds both polarities: a shipped coordinate rewritten as 4.4e2 must verify,
and a falsified one written the same way must not.

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

---------

Co-authored-by: 0xDarkMatter <0xDarkMatter@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -67,6 +67,8 @@ The helper refuses to run if the Claude and Codex versions already differ. If an
 | Dumbbell checker behaves (pass + adversarial cases) | `python3 scripts/test-verify-dumbbell.py` |
 | Slopegraph axes share one scale and every endpoint matches its printed value | `python3 scripts/verify-slopegraph.py --all` |
 | Slopegraph checker behaves (pass + adversarial cases) | `python3 scripts/test-verify-slopegraph.py` |
+| Ridgeline ridges share one amplitude and every printed range matches its bins | `python3 scripts/verify-ridgeline.py --all` |
+| Ridgeline checker behaves (pass + adversarial cases) | `python3 scripts/test-verify-ridgeline.py` |
 | Sankey flow conservation and ribbon geometry | `python3 scripts/verify-sankey.py --all` |
 | Sankey checker behaves (pass + adversarial cases) | `python3 scripts/test-verify-sankey.py` |
 | Generated icon assets are up to date (`icons.html`, `primitive-icons.md`) | `python3 scripts/build-icons.py` then `git diff --exit-code` on the two generated files |
@@ -107,6 +109,8 @@ python3 scripts/test-plugin-package.py \
   && python3 scripts/test-verify-dumbbell.py \
   && python3 scripts/verify-slopegraph.py --all \
   && python3 scripts/test-verify-slopegraph.py \
+  && python3 scripts/verify-ridgeline.py --all \
+  && python3 scripts/test-verify-ridgeline.py \
   && python3 scripts/verify-sankey.py --all \
   && python3 scripts/test-verify-sankey.py
 ```
@@ -118,6 +122,7 @@ python3 scripts/test-plugin-package.py \
 - **`verify-*.py`:** the extractor's real behavior no longer matches its fixture or the documentation, or the reference/command/prompt wiring drifted. Fix the source of truth — do not widen a test to avoid a failure.
 - **`verify-screenshot-freshness.py`:** a canonical minimal-light example or its committed PNG changed without a synchronized catalog refresh. Before the first regeneration, install the renderer with `python3 -m pip install playwright && python3 -m playwright install chromium`. Then run `python3 scripts/render-canonical-screenshots.py`, inspect all 39 renders, and commit the updated PNGs plus `docs/screenshots/manifest.json`.
 - **`verify-slopegraph.py`:** the two axes disagree about scale or origin, or an endpoint is drawn somewhere other than where its own declared value belongs. Fix the coordinate, never the label — and never move a point to stop two endpoint labels colliding, because crowded labels mean the values really are close.
+- **`verify-ridgeline.py`:** a ridge is drawn on its own amplitude, a baseline sits off the stack's pitch or away from its drawn rule, a ridge is sampled on its own x positions, or a printed range is wider than the bins it claims. Fix the geometry or the declaration so they state one thing — never renormalise a single ridge to make it readable, and never move a baseline to buy one ridge headroom.
 - **`verify-geometry.py`:** a label mask overlaps a node declared later in the document, so the node fill clips the label at render time. Move the label to a free segment of its connector — keep the 6–10px gap from the stroke required by SKILL.md §6, and do not shrink the mask to sneak under the check.
 - **Icon assets:** you changed `scripts/vendor/icons/` or `scripts/build-icons.py` and the generated files went stale. Rerun `python3 scripts/build-icons.py` and commit the regenerated files.