feat: add verified 3D density focus template

[hang-jin]

What changed

• add the public density_ridgeline3d workflow for 2–6 ordered conditions
• render two user-supplied precomputed density profiles plus one user-supplied baseline focal locator per condition
• add strict semantic/data gates, editable Origin rendering, preview parity, examples, bilingual documentation, and public gallery assets
• add exact Origin XYZ binding, axis, camera, source-integrity, and four-format verification

Why

A community request needs an editable Origin equivalent of a 3D dual-density figure with supplied focal locations, without inferring KDE, normalization, smoothing, thresholds, peaks, or intersections.

User impact

Users can select a verified 3D density-focus route when their mixed-wide table provides all six required roles. Ambiguous threshold-named columns remain confirmation-gated, and the original source remains unchanged.

Validation

• real Origin OPJU, PNG, PDF, and TIF generated
• 12/12 plots and 36/36 XYZ bindings read back successfully
• axis, camera, typography, source hash, and human visual QA passed
• 707 tests passed, 1 skipped
• CI-equivalent Ruff passed
• strict public-release audit: 651 files, 0 errors