Add Tigris sandbox connector

[davidmyriel]

Adds a sandbox connector for Tigris, the
globally-distributed S3-compatible object store.

Unlike the default in-memory sandbox, files written here persist across runs, so
an agent keeps its workspace between invocations.

The connector implements the
SandboxApi file methods over a Tigris bucket (@tigrisdata/storage) and exposes
checkpoint / list_checkpoints tools backed by @tigrisdata/agent-kit for cheap
whole-workspace snapshots (no extra buckets, nothing to clean up).

It is intentionally file-only: exec() throws with guidance to pair Tigris
with a VM provider (E2B/Daytona/Modal) when a real shell is needed.

flue add tigris generates connectors/tigris.ts in the user's project.

Validation: passes generate-connector-index.ts (registers on slug tigris);
embedded code typechecks against the real package types; unit tests cover all
file ops + the checkpoint tools; live smoke test against a real bucket passes.

[astrobot-houston]

Thanks for the contribution! We're closing this PR and moving the conversation to the existing thread: #86

We've moved to a model where bugs and feature proposals are discussed in issues/discussions before code review, so the community can help prioritize and shape the work. Your branch is linked from the new thread so the implementation isn't lost — please join us there to continue the conversation.

— astrobot 🤖