Add PaCMAP and LocalMAP dimensionality reduction algorithms

[patcon]

Closes #48

Summary

• Implements PaCMAP (Pairwise Controlled Manifold Approximation Projection) and LocalMAP as new DR algorithms, following the existing UMAP/TriMap stylistic patterns
• PaCMAP uses three explicit pair types (nearest-neighbor, mid-near, further) with a dynamic three-phase weight schedule and Adam optimization; initialized via PCA
• LocalMAP extends PaCMAP with embedding-space FP pair resampling in phase 3 for sharper local cluster separation
• Both algorithms are exported from the main package, have 17 new tests (9 for PaCMAP, 8 for LocalMAP) with full coverage across Node + Chromium + Firefox + WebKit via Playwright, and include VitePress doc pages with live IRIS visualizations
• All existing 1460 tests continue to pass

Reference

• Original Python implementation: https://github.com/YingfanWang/PaCMAP
• Paper: https://arxiv.org/abs/2012.04456

Test plan

• PaCMAP and LocalMAP unit tests pass across Node and all three browser environments
• Full test suite (1460 tests) passes with no regressions
• npm run build succeeds with no new type errors
• Doc pages render live IRIS scatter plots via the showcase grid

🤖 Generated with Claude Code (~200 words of PR description from ~230 words of human prompts across this session)

[patcon]

Ah shoot, the CLAUDE.md was accidentally committed here, but if you dislike that, I can remove it (it just helps people using these tools to save tokens)

Anyhow, I'm very happy to discuss or learn that such PRs are not welcome -- I've been using them for my own side-projects, but am new to how etiquette is developing for contributors, and this is my first go at that :)