Merge curated fork work: 12 new diagram types, icons, export, onboarding v2

Imports the substantive work from the aristide/diagram-design fork (PR #9)
as a curated set:

- 12 new diagram types with reference docs: radar, bar, line, gantt,
  scatter, it-state, high-level, process, medallion, data-flow,
  dp-integration, dp-security-matrix (26 types total)
- 86-icon monochrome IT/cloud primitive, build script, and gallery
- /diagram-design:export command with PNG/SVG export reference
- Onboarding v2: URL, skill, and folder design-token sources
- Mandatory connector rules (orthogonal elbows, label gaps, fanned
  attach points, bridge crossings) + architecture/ER connector upgrades
- Series palette tokens for multi-series chart types
- THIRD_PARTY_LICENSES.md covering Tabler, Simple Icons, log-z, Devicon

Not taken from the fork: plugin-manifest identity changes, the client-brand
takeover of style-guide.md, and client-branded example files. The six
affected type examples were regenerated in the neutral editorial skin with
generic content, and their README screenshots recaptured. Reference docs
for those types were rewritten to semantic tokens and typography roles.

Version: 1.0.0 -> 2.0.0.

Co-authored-by: Aristide <mendoo.aristide@gmail.com>

skills/diagram-design/references/style-guide.md

@@ -35,6 +35,20 @@ Every token is referred to by **semantic role**, not by its hex value. Type refe
 
 Any `rgba(28,25,23, X)` in light becomes `rgba(250,247,242, X)` in dark. Same opacities, RGB flipped. The accent gets a slight hue-shift brighter to read on dark paper.
 
+### Series palette (multi-series chart types only)
+
+A small set of desaturated, editorial-tone colors for chart types that genuinely need to distinguish multiple overlapping entities (currently: **radar**). The "1-focal" rule still holds — `accent` is reserved for the focal series; the palette below covers the rest.
+
+| Token | Light | Dark | Notes |
+|---|---|---|---|
+| `series-1` | `#7c8f6f` (sage) | `#9caf8f` | Non-focal series |
+| `series-2` | `#5e7a9b` (dusty-blue) | `#82a0c0` | Non-focal series |
+| `series-3` | `#b8915a` (mustard) | `#d3ad7a` | Non-focal series |
+| `series-4` | `#9c6b50` (rust-brown) | `#b88670` | Non-focal series |
+| `series-5` | `#6e6479` (slate) | `#8d8298` | Non-focal series |
+
+Fills sit at `0.18` opacity light, `0.22` dark; strokes use the full color. **Don't backfill these tokens to non-chart types** — architecture, swimlane, etc. continue to use muted-ink variants. The series palette is opt-in for diagrams where overlapping shapes demand distinguishable color, not a license to add color elsewhere.
+
 ---
 
 ## Typography