Align source color palette across hero globe and Interactive Explorer

[rdhyee]

Problem

The rotating globe on the homepage (assets/isamples_globe.webp) uses a different color palette from the Interactive Explorer and Progressive Globe tutorial. A user sees OpenContext as orange on the landing page, clicks through, and sees OpenContext as red in the explorer.

Palette mismatch

Source	Hero WebP (tools/globe_capture.html)	Explorer + tutorials
SESAR	#2196F3 Material Blue	#3366CC Google Blue
OPENCONTEXT	#FF9800 Orange	#DC3912 Red
GEOME	#4CAF50 Material Green	#109618 Google Green
SMITHSONIAN	#E91E63 Material Pink	#FF9900 Orange

Root cause: duplicated palette definitions

The same palette is copy-pasted in four places, with globe_capture.html having drifted:

• tutorials/progressive_globe.qmd (lines 209-216) — Google Charts Classic
• tutorials/isamples_explorer.qmd (lines 41-57) — Google Charts Classic
• tutorials/parquet_cesium_isamples_wide.qmd (~line 100) — Google Charts Classic
• tools/globe_capture.html (lines 96-101) — Material Design (drift)

Proposed fix

1. Extract palette to a single shared module (e.g. assets/js/source-palette.js) exporting SOURCE_COLORS and SOURCE_NAMES.
2. Import from all four consumers.
3. Re-run tools/capture_globe_rotation.py to regenerate assets/isamples_globe.webp with the canonical palette.

Canonical palette (matches explorer, which is the user-facing interactive view):

• SESAR: #3366CC
• OPENCONTEXT: #DC3912
• GEOME: #109618
• SMITHSONIAN: #FF9900