add architecture docs synced to current source and sdd process

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.

docs/architecture/decisions/001-html-agnostic-core.md

@@ -0,0 +1,31 @@
+---
+status: draft
+last_updated: 2026-05-18
+---
+
+# ADR-001: HTML-agnostic core
+
+**Status**: Proposed
+
+## Context
+
+UJSX is a universal JSX IR that treats JSX as an intermediate representation. The core types (UNode, UElement, UniversalProps) are deliberately free of any platform-specific concepts.
+
+## Alternatives Considered
+
+- **HTML-compatible props (className, onClick, etc.)**: Include DOM/HTML-specific prop names in core types. Rejected because it biases toward DOM rendering and forces non-DOM hosts to filter/translate irrelevant props.
+- **Separate "web" prop types**: Create a parallel type hierarchy for web/DOM props alongside the universal core. Rejected because it creates two type hierarchies and increases complexity for hosts that don't need HTML.
+
+## Decision
+
+UJSX core does NOT include HTML/DOM-specific concepts. No `onClick`, no `className`, no `style`, no `aria-*`. UniversalProps accepts any key-value pairs because different hosts need different prop shapes. The host decides what props mean.
+
+## Consequences
+
+### Positive
+- Clean separation. Each host defines its own prop semantics. Flowgraph hosts use `{ name, type, url }` not `{ className, id }`.
+- TypeBox schemas for host-specific props can validate independently. No "stripping" step needed.
+
+### Negative
+- Consumers targeting HTML must map their own props (e.g., `class` → `className`). This is the host's responsibility.
+- No built-in event handling system — events are host-specific. The event system (`PubSubLike`, `EventEnvelope`) is generic.