v0.2.9

Merge branch 'seankcw:main' into main

Forty-four commits: the git-read work that took a board poll from 700ms to 70ms
and got the CLI spawn off the first page load, namespaces as the organising idea
across the nav, the index, the board and a page of their own, three ways to read
a spec, and the documents a store files beside its specs.

package.json is the only conflict, and the same one every sync here has: the
version stays 0.2.5 and the pnpm pin stays, since both are this fork's and
neither is upstream's to set. The description and the mermaid dependency come
from upstream, which is where they were changed.