Add SDD architecture docs for dbtype

Phase 0 architecture specification following the alkdev documentation
pattern from @alkdev/flowgraph. Documents the validated architecture
(UJSX elements → Type.Module → Drizzle hosts) based on e2e probe results.

Docs added:
- README: Project overview, architecture, current state
- architecture/README: Index, design decisions, relationships
- architecture/schema: Type.Module as bundle, construction, serialization
- architecture/hosts: HostConfig per dialect, column mapping, symbolic defaults
- architecture/elements: UJSX element types, props, function components
- architecture/module: Module mechanics, format registration, diffing
- architecture/repo-adapter: from-dbtype operations adapter (phase 2)
- architecture/build-distribution: Package structure, exports
- architecture/open-questions: 10 open questions across all topics
- ADRs 001-005: UJSX as IR, Type.Module, HostConfig, format, repo adapter

docs/architecture/build-distribution.md

@@ -0,0 +1,91 @@
+---
+status: draft
+last_updated: 2026-05-22
+---
+
+# Build & Distribution
+
+Package structure, exports, dependencies, and tree-shaking strategy.
+
+## Package
+
+- **Name**: `@alkdev/dbtype`
+- **Type**: ESM with CJS fallback
+- **Peer dependencies**: `@alkdev/typebox >=0.34.49`, `@alkdev/ujsx >=0.1.0`, `drizzle-orm >=0.36.0`
+- **Dev dependencies**: All three peer deps for testing, plus `tsx`, `vitest`, `typescript`
+
+## Sub-path Exports
+
+```json
+{
+  "exports": {
+    ".": {
+      "import": { "types": "./index.d.mts", "default": "./index.mjs" },
+      "require": { "types": "./index.d.cjs", "default": "./index.cjs" }
+    },
+    "/core": {
+      "import": { "types": "./core/index.d.mts", "default": "./core/index.mjs" },
+      "require": { "types": "./core/index.d.cjs", "default": "./core/index.cjs" }
+    },
+    "/sqlite": {
+      "import": { "types": "./sqlite/index.d.mts", "default": "./sqlite/index.mjs" },
+      "require": { "types": "./sqlite/index.d.cjs", "default": "./sqlite/index.cjs" }
+    },
+    "/pg": {
+      "import": { "types": "./pg/index.d.mts", "default": "./pg/index.mjs" },
+      "require": { "types": "./pg/index.d.cjs", "default": "./pg/index.cjs" }
+    },
+    "/mysql": {
+      "import": { "types": "./mysql/index.d.mts", "default": "./mysql/index.mjs" },
+      "require": { "types": "./mysql/index.d.cjs", "default": "./mysql/index.cjs" }
+    }
+  }
+}
+```
+
+Tree-shaking: Users who only use SQLite import `/sqlite` and never pull in PG or MySQL column builders.
+
+## Source Structure
+
+```
+src/
+  core/
+    elements.ts          # h() wrappers, createComponent for table/column/index/fk
+    schema.ts            # extractTable, createSelectSchema, createInsertSchema, createUpdateSchema
+    module.ts            # buildModule, module construction helpers
+    column-types.ts      # DbColumnType union, colToTypeBox mapping
+    defaults.ts          # Symbolic default resolution ('now', 'uuid', 'autoincrement')
+    guards.ts            # Type guards for element types
+    index.ts
+  hosts/
+    sqlite.ts            # HostConfig for drizzle-orm/sqlite-core
+    pg.ts                # HostConfig for drizzle-orm/pg-core
+    mysql.ts             # HostConfig for drizzle-orm/mysql-core
+  repo/
+    from-dbtype.ts       # FromDbType adapter for @alkdev/operations (phase 2)
+    filters.ts           # Filter schema generation per column type
+    handlers.ts           # CRUD handler generation
+  index.ts               # Re-exports core
+```
+
+## Dependencies
+
+```
+@alkdev/dbtype
+├── @alkdev/typebox (peer)    # Type.Module, Type.Ref, Value.Check, FormatRegistry
+├── @alkdev/ujsx (peer)       # h, createComponent, HostConfig, createRoot
+└── drizzle-orm (peer)        # Dialect-specific column builders (per sub-path)
+```
+
+The core package (`@alkdev/dbtype/core`) depends only on `@alkdev/typebox` and `@alkdev/ujsx`. The dialect modules (`/sqlite`, `/pg`, `/mysql`) add `drizzle-orm` as a peer dependency (scoped to the specific dialect sub-module).
+
+## Constraints
+
+- **Core must not import from drizzle-orm** — the core (elements, schema extraction, module) is dialect-agnostic
+- **Dialect modules must not import from each other** — SQLite host doesn't pull in PG types
+- **Build is ESM-first** — CJS is generated as a fallback for compatibility
+
+## References
+
+- Typemap sub-path exports pattern: `docs/research/typemap-architecture.md`
+- Current package: `package.json`