feat: add simple versioning + sandbox mode

[forestileao]

Summary

This PR implements the scoped canvas versioning system end-to-end across backend, frontend, and CLI, and removes extra POC behavior that was out of scope (BY NOW).

The flow is now intentionally simple:

• Canvas structure lives in versions.
• Each canvas has one live_version.
• Each user has one draft version.
• Change request creation snapshots the current draft and publishes it.
• Sandbox mode bypasses versioning and edits live directly.

Backend

• Moved canvas nodes and edges ownership to canvas versions.
• Updated canvas model so it keeps only a non-null live_version_id relation.
• Implemented per-user unique DRAFT version behavior.
• Simplified change request model/flow:
  • Kept only create/publish flow required by product scope.
  • Change request stores title, description, and snapshot_version from draft at creation time.
• Removed non-required conflict/version-control complexity:
  • no base version/revision conflict flow.
  • removed extra RPCs/handlers that were not requested (close/resolve/sync/discard APIs).
• Added/updated authorization for only the required versioning endpoints.
• Added sandbox mode support in backend behavior:
  • when sandbox is disabled, live update requires version flow.
  • when sandbox is enabled, live direct updates are allowed.

Frontend

• Brought in the versioning sidebar behavior (without bringing the separate versioning page flow).
• Create Change Request action now opens modal and publishes directly from there.
• Added history UX for live/current + past published versions.
• History actions now use explicit icon actions:
  • open/view version
  • open diff modal against previous version
• Reworked diff UI to GitHub-style component rendering (react-diff-view) and removed earlier custom/terminal-like output.
• Diff modal now shows change request metadata (title + markdown-rendered description) and uses larger dimensions.
• Updated header/edit-mode behavior:
  • versioning mode: explicit edit entry, save state dropdown, autosave toggle, save/undo actions, discard/exit edit actions.
  • sandbox mode: warning label + versioning disabled behavior.
  • added “Pending Draft” warning when draft differs from live outside edit mode.
• Fixed dropdown interaction behavior to close on internal actions.
• Ensured canvas data refreshes correctly when re-entering live/version context.

CLI

• Kept sandbox mode API behavior backward-compatible for canvases update.
• Added non-sandbox versioning flow:
  • require draft flow for updates (instead of direct live updates),
  • support publish command from draft/versioning flow.
• Added explicit error when trying to update live canvas while org is not in sandbox mode.

Migrations / Data Model

• Reworked migrations to match scoped design (clean implementation, no POC leftovers).
• Ensured schema aligns with required behavior only (no conflict/revision columns).

Tests / Fixes

• Updated failing tests to new versioned canvas structure (live_version instead of direct canvas.edges/nodes).
• Fixed unit/e2e breakages caused by live_version_id non-null requirements.
• Updated related setup/fixtures to create valid live versions for canvases.

Scope Control

• Removed features and API surface not requested in the original scope.
• Kept implementation focused on required versioning behavior only.

[superplanehq-integration]

👋 Commands for maintainers:

• /sp start - Start an ephemeral machine (takes 3m)
• /sp stop - Stop a running machine (auto-executed on pr close)

[forestileao]

/sp start

[superplanehq-integration]

This action is only available to maintainers.