feat: add snapshot in py server

[kerthcet]

What this PR does / why we need it

Which issue(s) this PR fixes

Fixes #

Special notes for your reviewer

Does this PR introduce a user-facing change?

[Copilot]

Pull request overview

This PR introduces snapshot operations (create/restore/list/find/get/delete) to the SandD daemon and exposes them through the Python server API, backed by new protocol message variants and expanded end-to-end tests.

Changes:

• Added snapshot message types to the WebSocket protocol and implemented snapshot request handling in the daemon.
• Added Python-facing snapshot APIs and a SnapshotInfo model to represent snapshot metadata.
• Updated snapshot manager/types naming and expanded E2E coverage for snapshot workflows.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
server/src/lib.rs	Adds PyO3-exposed snapshot methods that send snapshot protocol messages and await responses.
sandd/src/snapshot/types.rs	Renames snapshot field to workspace (from workspace_path).
sandd/src/snapshot/manager.rs	Renames find_by_tag to find_snapshot_by_tag and changes get_snapshot to return SnapshotInfo.
sandd/src/protocol.rs	Adds snapshot-related protocol message variants.
sandd/src/main.rs	Wires SnapshotManager into the daemon message handler and implements snapshot operations.
python/sandd/server.py	Adds Python API methods for snapshot operations and maps raw results into SnapshotInfo.
python/sandd/models.py	Introduces SnapshotInfo Python model (including timestamp handling).
python/tests/test_e2e.py	Adds extensive E2E tests for snapshot create/list/find/get/restore/delete behaviors.
examples/snapshot_simple.rs	Updates example code to the renamed find_snapshot_by_tag API.
docs/proposals/SNAPSHOTS.md	Updates the proposal doc with snapshot protocol integration details and renamed APIs.

Comments suppressed due to low confidence (1)

docs/proposals/SNAPSHOTS.md:199

• The proposal still documents get_snapshot returning a full Snapshot, but the implementation now returns SnapshotInfo (see sandd/src/snapshot/manager.rs). The doc should match the implemented API.

    /// Get snapshot by ID
    pub async fn get_snapshot(&self, id: &str) -> Result<Snapshot>;

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[kerthcet]

/kind feature

[kerthcet]

/lgtm

[InftyAI-Agent]

Approved: PR has both lgtm and approved labels