Make the README a concise project entry point

[bcomnes]

Problem

The README is over 3,000 lines and serves as both the initial introduction and detailed feature reference.
New users must navigate a large amount of material to establish the core source-to-output model.
The opening copy also contains spelling and clarity problems, including ande and technolgies.

The existing reference material and examples are valuable, so the goal is to improve navigation while preserving their availability.

Proposed direction

Keep the README focused on the product's purpose, installation, a minimal successful build, the filesystem/page model, one representative source-to-output example, and links to further documentation.

Move detailed reference sections into focused documents under docs/ that are also reachable from the generated documentation site.
Organize those documents around pages/layouts/variables, assets and clients, generated pages/templates, manifests/service workers, and the programmatic API as appropriate.

Perform an editorial pass on the retained introduction and moved material.
Check existing section links and provide an anchor/link compatibility strategy for moved sections.

Acceptance criteria

• A new user can install DOMStack and build a basic site using the README alone.
• The core conventions and source-to-output example are easy to locate.
• All existing detailed reference content remains available through clear links.
• Internal links, important existing README anchors, and documentation-site navigation are preserved or updated deliberately.
• The documentation site still builds successfully.
• Markdown prose uses one sentence per line.

Sequencing

Follow the functional work independently.
Coordinate with existing documentation and migration issues, including #271, without duplicating the v12 migration guide.