feat(call-center): adopt v19.1 flow features

[siarheihuzarevich]

Summary

• refactor the Call Center example around FFlowState, typed domain records, persistence, and focused Angular components
• enable the current accessibility, control-scheme, unified connector, and reflow-on-resize APIs
• batch expand/collapse with asynchronous resize reflow so it produces one undo history item
• update the portal, README, generated search/LLM content, and AI guidance for the state and reflow patterns
• bump the flow and layout package metadata to 19.1.2

Core fixes

• use resolved sourceSide / targetSide values in worker redraw payloads so connections keep the correct geometry after state-driven node movement
• resolve the nearest unified connector for drag and click connection creation; nested source connectors are no longer shadowed by a target connector on the node host
• add regression coverage for worker endpoint sides and nested connector creation, including Shadow DOM

Impact

The Call Center example now demonstrates the supported v19.1 architecture instead of maintaining its own graph store. Expand/collapse reflow participates in history as one action, state survives reloads, connection geometry remains current, and new connections work when node hosts are also target connectors.

Validation

• NX_DAEMON=false npx nx test f-flow --watch=false --browsers=ChromeHeadless --skip-nx-cache (290 tests)
• NX_DAEMON=false npx nx lint f-flow --skip-nx-cache
• NX_DAEMON=false npx nx lint call-center --skip-nx-cache
• NX_DAEMON=false npx nx build call-center --configuration development --skip-nx-cache
• browser verification of connection creation/removal, undo/redo, resize reflow, forms, and connection redraw