feat: assemble the open-source pages from lancedb/lancedb

[jackye1995]

A3 of the documentation migration. The open-source pages move to lancedb/lancedb#4122 and are assembled from there.

Merge order: #352 → this → and lancedb/lancedb#4122 must land first, since CI assembles from that repository's main.

What moves and what stays

102 pages, the static assets, the generated snippets and the test suite they come from all move to lancedb/lancedb/docs/web. This repository keeps what it still owns: the Geneva pages until Stage G replaces them, the generated dataset cards, the OpenAPI spec, and the Enterprise pages until A5 moves them to sophon.

Navigation is the interesting part

It is authored once, in the root that owns the pages, so that root can be served on its own — a contributor runs mint dev in docs/web with no second checkout. Everything this repository still holds is contributed as a fragment saying where each entry belongs: the chain of groups above it and the sibling it follows.

Appending was not good enough. Sidebar order is what a reader navigates by, and appending dropped Geneva below Support and Datasets past Use Cases — a silent reordering of the whole site.

scripts/split_nav.py generates that fragment by walking the original navigation rather than by hand. That is why it contains six entries rather than ninety-seven: a container that moves wholesale is carried across intact instead of rebuilt from its children. A5 reuses it when the Enterprise pages move.

Three things that had to match exactly

Each was caught by the harness, not by review:

• The openapi block names a spec file this repository owns, and Mintlify refuses to build at all when it is missing. It is lifted out of the base navigation and restored by the fragment.
• Key order in docs.json is load-bearing. Mintlify hashes its CSS and JS bundles from those bytes, so moving navigation renamed every asset on every page — 179 differences from one reordered key.
• ensure_ascii likewise. The banner text carries an em-dash; escaping it differently changed the same bytes.

CI

Now checks out lancedb/lancedb@main and assembles twice, comparing the two. The site no longer exists as a single tree anywhere, so comparing the assembly against docs/ is no longer available — determinism is what the comparison can still establish, and a stale stored baseline is exactly what this harness was built to avoid.

Verified

• assembled tree byte-identical to the one it replaces — diff -rq clean against the pre-move source
• two consecutive assemblies identical
• full mint export comparison: VERDICT: EQUIVALENT, zero real differences
• link check clean
• the standalone site in lancedb/lancedb builds and renders all 102 pages