chore: add changeset for unified Store refactor (#38)

.changeset/unified-store-refactor.md

@@ -0,0 +1,24 @@
+---
+"@ocas/core": minor
+"@ocas/fs": minor
+"@ocas/cli": minor
+---
+
+Unified Store type refactor (#38)
+
+**Breaking changes:**
+
+- `Store` is now `{ cas: CasStore, var: VarStore, tag: TagStore }` — all sub-stores accessed via properties
+- `bootstrap(store)` and `putSchema(store, schema)` are now **synchronous** (were async)
+- `VariableStore` class removed from `@ocas/core` — SQLite implementation moved to `@ocas/fs`
+- `createVariableStore()` removed from `@ocas/core`
+- `openStoreAndVarStore()` removed from CLI internals — use `openStore()` returning unified `Store`
+- `RenderOptions.varStore` removed — templates resolved via `store.var` internally
+- `@ocas/core` has zero `bun:sqlite` imports — pure TypeScript
+
+**New:**
+
+- `CasStore`, `VarStore`, `TagStore` sub-store types
+- `TagStore` — first-class tags on any CAS node (not just variables)
+- `var-store-helpers.ts` — shared validation/history logic
+- `validation.ts` — shared `validateName()` exported from core