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>

.factory-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "diagram-design",
   "description": "Create branded architecture, IT current-state, flowchart, sequence, state machine, ER/data model, timeline, swimlane, quadrant, radar/spider, polar chart (polar/radial lollipop), loop/flywheel, nested, tree, org chart, layer stack, Venn, pyramid/funnel, treemap, bar, line, Gantt and scatter charts, high-level, process, medallion, data flow, DP integration, DP security matrix, sankey, fishbone, Wardley map, kanban, user journey, deployment, dependency graph, UML class, story map, or database schema diagrams as standalone HTML/SVG/PNG. Redraw .drawio/.drawio.png/.drawio.svg or Mermaid .mmd sources at a chosen size/detail; onboard brand tokens from a website; add semantic patterns, callouts, accessible motion, or sketchy/hand-drawn styling.",
-  "version": "2.6.4",
+  "version": "2.6.5",
   "author": {
     "name": "Cathryn Lavery",
     "url": "https://github.com/cathrynlavery"