feat(scatter): add bubble variant for three-value comparisons (#141)

* feat(scatter): add bubble variant for three-value comparisons

Bubble chart as a Scatter variant per the issue #62 triage: x and y on
shared zero-based linear scales, bubble AREA proportional to the third
value (r = K*sqrt(size)), one accent bubble, ink-opacity ramp as ink-mass
compensation, largest-first paint order.

scripts/verify-bubble.py derives both axis scales and the area constant
from the set itself (Theil-Sen, leave-one-out) and holds every bound
label and tick against the mark it describes; test-verify-bubble.py
exercises both polarities. Bindings are bubble-specific (data-size,
data-name, data-tick) rather than data-series, so verify-slopegraph.py
never claims a bubble file and neither checker needs scope carve-outs.

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

* fix(bubble): report a bubble whose peers cannot describe a scale

A bubble holding the only distinct value on an axis was skipped by the
leave-one-out residual test — its own fit is degenerate, and the full-set
fit passes through wherever it was drawn, so a wrong coordinate shipped
clean. Report it as unverifiable instead of skipping it.

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

* chore: bump to 2.6.3 and register bubble gates

Ridgeline (#143) landed on 2.6.2, colliding with this branch's bump, so
re-bump past it. Also add the bubble gate commands to the maintainer
policy's local_commands, matching what ridgeline registered.

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

* chore: bump to 2.6.5

The mermaid fix (#131) landed on 2.6.4, colliding with this branch's
bump again. Re-bump past it.

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

---------

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

CONTRIBUTING.md

@@ -71,6 +71,8 @@ The helper refuses to run if the Claude and Codex versions already differ. If an
 | 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` |
+| Bubble positions sit on shared axis scales and area encodes every declared size | `python3 scripts/verify-bubble.py --all` |
+| Bubble checker behaves (pass + adversarial cases) | `python3 scripts/test-verify-bubble.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 |
 
 The semantic-pattern gate also caps `skills/diagram-design/SKILL.md` at 40,000 bytes so the installed skill remains practical to load. If that gate fails, reduce duplication or move detail into a routed reference; do not remove routing vocabulary from frontmatter.
@@ -112,7 +114,9 @@ python3 scripts/test-plugin-package.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
+  && python3 scripts/test-verify-sankey.py \
+  && python3 scripts/verify-bubble.py --all \
+  && python3 scripts/test-verify-bubble.py
 ```
 
 ### If a gate fails
@@ -123,6 +127,7 @@ python3 scripts/test-plugin-package.py \
 - **`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-bubble.py`:** a bubble is drawn off the shared axis scale its peers describe, its radius disagrees with the one area constant (`r = K·√size`), a second bubble wears the accent, an overlapping smaller bubble is painted under a larger one, or a bound label/tick disagrees with the mark it names. Fix the geometry, never the binding — and never nudge a bubble to open up space, because crowded bubbles mean the values really are close.
 - **`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.