Updated Software Design Document (markdown)
Version references: 2.0.0-beta.2 documentation release
Fix Mermaid parse errors (semicolons) and two broken table rows
Restructure wiki: landing page, ADD, SDD, workflow diagrams and archived 1.1.3 docs
* Home.md: documentation hub that routes between the current 2.0.x line
(branch ha2026_09_dev) and the archived 1.1.3 line, plus a capability matrix
* Architecture-Design-Document.md: ADD for 2.0.x with requirements, context,
component decomposition, 14 architectural decisions, cross-cutting concerns,
deltas versus 1.1.3, quality attributes, risks and extension points
* Software-Design-Document.md: SDD for 2.0.x with the module inventory, class
view, five interface contracts, component design, sequence diagrams, the
persistence data model, error handling matrix, localisation, build/verify/
release process and the traceability matrix
* Workflow-Diagrams.md: the GitDiagram repository map (15 components, 23
connections) with a provenance note, the authored 2.0.x component map and the
setup, polling, range query, write, export, conflict and record-state flows
* Archive-1.1.3-Design-Documentation.md: the former Developer & Technical
Reference Guide preserved verbatim (and converted back to Markdown so it
renders again) with an archive banner and the list of defects fixed in 2.0.x
* Developer-&-Technical-Reference-Guide.md: pointer page so old links keep working
* _Sidebar.md: navigation for both documentation lines