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/agent-builtin/src/detail.ts

@@ -32,7 +32,7 @@ export async function storeBuiltinDetail(
 
   const turnHashes: string[] = [];
   for (const turn of turns) {
-    const hash = await store.put(schemas.turn, turn);
+    const hash = await store.cas.put(schemas.turn, turn);
     turnHashes.push(hash);
   }
 
@@ -44,6 +44,6 @@ export async function storeBuiltinDetail(
     turnCount: turnHashes.length,
     turns: turnHashes,
   };
-  const detailHash = await store.put(schemas.detail, detail);
+  const detailHash = await store.cas.put(schemas.detail, detail);
   return { detailHash, turnCount: turnHashes.length };
 }