feat(agentflow): add node execution visualization with HITL support (#6312)

* Integrate executuons API

* Fix Status indicators example to use AgetnContext

* Fix styling of HITL pause icon

* Tet changes for node executiom

* Fix lint error

* Chat panel implementation

* Import functionality from v2

* Fix proxy issues for chat

* Fix styling of chat

* Split out chat panel changes — execution UI only

Remove TestFlowDialog, TestFlowButton container, chat avatars, react-markdown/remark-gfm/fetch-event-source deps, uuid/fileMock mocks, and related vite proxy changes. These belong to feat-agentflow-chatpanel which will be opened on top of this branch.

Restore StyledFab to node-palette, restore old TestFlowButton component, and revert Agentflow.tsx/canvas index to pre-chat state so this branch contains only the node execution status UI work.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore(agentflow): remove TestFlowButton placeholder from execution branch

TestFlowButton belongs to the chat panel PR. Removing the placeholder
component, its exports, and its usage in Agentflow.tsx so this branch
contains only execution UI work.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Add test changes

* FIx gemini comments

* Add dark mode toggle

* Remove Execution API references

* Update E2E to stream API responses

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>