fix: stabilize node flows and dashboard tabs

[numnx]

Summary

Fixes the Nodes page validation failure and intermittent dashboard freezes, especially when several dashboard tabs are open or a tab has spent time in the background.

Root causes

• Legacy canvas starter nodes were imported with obsolete node types and port handles, producing the three graph validation errors.
• The node-definition detail endpoint returned a flattened catalog summary while the inspector expected the full nested manifest, which could trigger a render failure loop.
• Canvas dragging propagated a full-page state update on every pointer event.
• Background tabs retained WebGL animation, realtime sockets, and fallback polling, allowing resource contention to accumulate across tabs.
• Overlapping asynchronous flow loads and validations could apply stale results after navigation or project changes.

Changes

• Migrate legacy canvas node types, handles, and safe metadata to current registered definitions.
• Return the full node manifest from the detail endpoint while preserving the compact catalog response.
• Make the inspector tolerant of older flattened responses.
• Keep drag previews local, coalesce pointer movement with animation frames, and commit graph state on release.
• Suspend animated backgrounds on the Nodes page and release WebGL/realtime/polling resources while tabs are hidden.
• Guard node-flow actions and validation against stale or unmounted requests.
• Document node-flow compatibility and dashboard background-tab behavior.
• Add backend and dashboard regression coverage for each failure mode.

Validation

• pnpm run lint
• pnpm run test:backend — 5,451 passed, 7 skipped
• pnpm run test:dashboard — 2,149 passed, 2 skipped
• pnpm run build
• Feature-enabled production build with Nodes, node-flow backend, and automation security enabled
• Live three-tab dashboard check: no page errors, no retained WebGL canvases, and responsive tab switching
• Live add-node, drag, navigate away, and return check: responsive with no page errors

Risk and rollback

Risk is localized to node-flow serialization/detail responses and dashboard resource lifecycle behavior. The catalog list contract remains unchanged, and the inspector retains compatibility with flattened detail data. Roll back this commit if node-definition consumers or tab reconnection behavior regress.