Phase 1 of SDD process: syncing docs/architecture/ to reflect the
existing source code. Eight component documents describe WHAT and WHY
(not HOW) for each module: schema, element factory, reactive layer,
host config, transforms, events, pointers, and build distribution.
Three ADRs capture key decisions (HTML-agnostic core, TypeBox Module
as type registry, Preact signals-core for reactivity). Each doc
documents known reconciler gaps and references the research in
docs/research/reconciler/.
Also adds docs/sdd_process.md (process reference shared across
alkdev projects) matching the taskgraph_ts pattern.
