Add a TypeScript and Python public API crosswalk

[reacher-z]

Context

Graph Engineering intentionally implements one portable Graph IR in two native runtimes. New users need a compact map between equivalent public APIs and result shapes.

Scope

Add a documentation page mapping Graph models, compilation, canonical hashing, graph execution, cancellation, barrier evaluation, route selection, events, and checkpoints between TypeScript and Python.

Acceptance criteria

• Link every name to its source package or Python module.
• Mark exact semantic parity, naming-only differences, and unsupported surfaces separately.
• Include one side-by-side minimal snippet that consumes the same Graph IR.
• Do not claim scheduler-applied routing or durable resume exists today.
• Add the page to the root documentation index and pass the link checker.