PR #647 - preloopdev/preloop

Summary

Restructure the Mintlify site into Overview, Control plane, and Runner tabs.
Replace long pasted design documents with shorter task-oriented pages.
Refresh public architecture diagrams with Graphviz .dot sources and SVG exports.
Document the current main-branch microVM pool (preloop-orchestrator → preloop-vm → SmolVM/AgentENV providers).
Restore and embed the repository's demo recordings in the introduction, quickstart, and debugging guide.
Move contributor-only trackers and implementation plans under docs/contributing/ and exclude them from Mintlify.
Correct stale documentation links in runtime help, runner-watch, contributor docs, migrations, and repository guidance.

The unmerged sandbox-service draft is preserved locally on the docs/site-rework-open-prs branch and is intentionally not included in this PR.

Diagram scope

Included:

system overview
control plane
runner protocol
job lifecycle
workflow parser
expression engine
microVM pool
observability
debug sessions
runner listener/worker

Intentionally excluded: sandbox-service, hosted-plane diagrams, hosted job lifecycle, container-build, and provider-internal SOMAC/VOWIN details.

Source of truth

Published docs describe public/main only. Unmerged PR-only behavior such as the sandbox-service CLI, actions policy, and JIT runner configuration was removed from the active docs.

Review fixes

Retargeted runtime error/help paths to the new documentation locations.
Fixed runner-watch's relocated fidelity tracker path and README link generation.
Converted contributor-doc links to repository-relative paths.
Restored deleted demo media and attached it to the relevant docs.

Verification

mint validate
mint broken-links --check-anchors
mint a11y
just docs-diagrams
git diff --check
cargo check --locked -p preloop-runner-server -p preloop-cli -p preloop-runner -p preloop-vm -p preloop-conformance -p preloop-gha-parser
cargo test --locked -p runner-watch
cargo test --locked -p preloop-gha-parser --lib
cargo check --locked -p preloop-vm --tests

All checks passed. Mintlify reported only existing brand-color contrast warnings; no accessibility issues remained.