docs: restructure architecture docs to flowgraph pattern

- Create decisions/ directory with 32 numbered ADRs (ADR-001 through ADR-032)
  extracted from inline DD/SD/ED/SE decision sections
- Create open-questions.md with 16 OQs organized by theme, cross-referenced
  to ADRs, with status tracking (resolved/open)
- Create README.md as architecture index with doc table, ADR table, and
  lifecycle status definitions (draft/reviewed/stable/deprecated)
- Replace inline decision sections in all spec docs with ADR reference tables
- Replace inline open questions with OQ references to centralized tracker
- Update frontmatter: metagraph-module.md, overview.md, sqlite-host.md → reviewed;
  schema-evolution.md and encrypted-data.md remain draft
- DD1-DD10 → ADR-009 through ADR-018
- D1-D8 → ADR-001 through ADR-008
- SD1-SD5 → ADR-019 through ADR-023 (SD5 folded into ADR-006/008)
- ED1-ED5 → ADR-023 through ADR-027
- SE1-SE5 → ADR-028 through ADR-032

docs/architecture/decisions/006-enum-pattern-as-const-objects.md

@@ -0,0 +1,24 @@
+# ADR-006: Enumeration pattern — `as const` objects, not TypeScript enums
+
+## Status
+
+Accepted
+
+## Context
+
+TypeScript `enum` causes JSR slow-type issues and doesn't integrate well with TypeBox schemas. Enumeration values need to be available both as runtime constants and as TypeBox union literals.
+
+## Decision
+
+All enumerations use the `as const` object pattern (e.g., `GRAPH_STATUS = { Active: "active", ... } as const`). TypeBox schemas use `Type.Union` of `Type.Literal` values derived from the const object.
+
+## Consequences
+
+- No JSR slow-type warnings
+- Enum values available as both runtime constants and type system literals
+- Consistent pattern across the codebase
+- Matches the pattern used in `common.ts` for `ACTOR_TYPE`
+
+## References
+
+- [sqlite-host.md](../sqlite-host.md)