Add Morgan–Tian dependency graph studio

[Spring-1211]

Summary

• add the Morgan–Tian Poincaré dependency graph as an independent runnable web project
• provide 17-node proof-spine and 35-module DAG views with theorem focus interactions
• encode conservative Mathlib support evidence independently from mathematical lanes
• commit a validated read-only snapshot with 683 mapped statements
• include the dependency-graph specification, tests, local setup guide, and visual QA evidence

Location

website/dependency-graph-studio/

The existing Lean project, blueprint sources, and documentation are unchanged.

Verification

• npm run lint
• npm run data:validate
  • 17 coarse nodes
  • 35 medium-grain modules
  • 683 mapped statements
  • both graphs are directed and acyclic
• npm test
  • production build passes
  • 6 tests pass
• repository workflows
  • Blueprint: passed
  • Pending theorem audit: passed

Known repository baseline

Lean CI fails before building because the repository does not contain a
root-level lake-manifest.json. The same workflow already fails on the current
main commit for the same reason. This PR only adds files below
website/dependency-graph-studio/ and does not modify Lean configuration.

Data policy

The site runs from committed snapshots. The optional import command reads an
allowlisted subset from an existing research directory through
POINCARE_RESEARCH_ROOT; it does not modify the source directory or commit
maintainer-specific absolute paths.