chore: migrate from bun to pnpm + vitest + esbuild

- Replace bun:test with vitest across all packages
- Replace bun build with esbuild
- Replace bun:sqlite with better-sqlite3
- Fix OCAS Store API: store.put/get → store.cas.put/get
- Fix vitest vi.mock hoisting (vi.hoisted)
- Add pnpm-workspace.yaml and pnpm-lock.yaml
- Update all package.json test/build scripts

WIP: 8 failures remain in agent-hermes (bun engines check + sqlite migration)

Refs #26

packages/cli/src/__tests__/thread-show-status.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, test } from "bun:test";
+import { describe, expect, test } from 'vitest';
 import { mkdir, rm, writeFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
@@ -96,15 +96,15 @@ async function insertStepNode(
   const head = headEntry.head;
 
   const outputSchemaHash = await putSchema(uwf.store, OUTPUT_SCHEMA);
-  const outputHash = await uwf.store.put(outputSchemaHash, outputPayload);
-  const detailHash = await uwf.store.put(uwf.schemas.text, "detail-placeholder");
+  const outputHash = await uwf.store.cas.put(outputSchemaHash, outputPayload);
+  const detailHash = await uwf.store.cas.put(uwf.schemas.text, "detail-placeholder");
 
-  const headNode = uwf.store.get(head);
+  const headNode = uwf.store.cas.get(head);
   if (headNode === null) throw new Error(`head ${head} not found`);
   const isStart = headNode.type === uwf.schemas.startNode;
   const startHash = isStart ? head : (headNode.payload as { start: CasRef }).start;
 
-  const stepHash = (await uwf.store.put(uwf.schemas.stepNode, {
+  const stepHash = (await uwf.store.cas.put(uwf.schemas.stepNode, {
     start: startHash,
     prev: isStart ? null : head,
     role,