Packaging conventions (build from src/, stage, validate, package)

Question

Establish packaging conventions:

• The package is built from src/, never assembled by hand. A hand-assembled package is correct exactly once.
• Build into dist/, from a clean staging directory. Staging exists so the package contains what the format requires and nothing else:

rm -rf stage && mkdir -p stage
cp -r src/<artifact> stage/
<validate>            # Format check before packaging, not after.
<package> stage/<artifact> dist/
rm -rf stage

• The build command lives in the repository, in scripts/ when more than a couple of lines, and in docs/how-to/release.md either way.
• Version in exactly one place. Wherever the format keeps it — package manifest, frontmatter, module constant. Every other mention is derived or a duplicate waiting to go stale. CHANGELOG.md is the human-readable projection.

Decision needed: Document build process, create staging scripts, ensure version single-source-of-truth.

Label: wayfinder:task
Part of #2517
Blocks: #2518

Start by reviewing the existing src/ tree, scripts/, docs/how-to/release.md, package manifest, and CHANGELOG.md to identify current packaging and version locations. Establish the documented build flow through a clean staging directory, add scripts where needed, and ensure the package format is validated before packaging with one source of truth for the version.