Add PCA for visualization

[robertvava]

Objective

Implement PCA for visualization in addition to UMAP. This could be configured by a user in dataset.compute_visualization(method="pca").

Proposed strategy

Depending on mapping types, we could employ different implementations:

euclidean → euclidean: Standard PCA, normalize to [-1, 1]
euclidean → poincare: Standard PCA, then normalize into disk (e.g., tanh scaling)
hyperboloid → euclidean: logmap_0 to tangent space, PCA, normalize to [-1, 1]
hyperboloid → poincare: logmap_0 to tangent space, PCA to 2D, expmap_0 back to B^2

Acceptance criteria

• compute_visualization(method="pca") runs without error
• All mapping types can produce a graph
• Minimal test suite for this method
• Sufficient error catching with verbose logs for users

[mnm-matin]

there is a also a drop down picker option in the frontend for projection method...

[mnm-matin]

closed with #24