Add sandbox-scoped listing endpoints and schemas
- Implement handlers for files, secrets, variables and volumes with DB
queries, auth checks, retries and presentation transforms
- Add sandboxId query param to lexicons, pkl types and generated TS
types; support offset/limit pagination
- Add fileView and extra volume fields (path, readOnly, createdAt,
updatedAt) to schemas and types
- Add DB migrations and schema updates (created_at/updated_at, sandbox
volume name) and adjust drizzle schemas
- Update web hooks, types and pages to pass sandboxId/offset/limit and
add pagination and small UI tweaks