EvalNode — Inline Output Quality Gate for AgentFlow V2

[NithiN-1808]

hey folks! been building with Flowise for a while and hit a wall, once a flow is in production, there's no way to catch bad LLM output before it reaches the user. the cloud eval feature is awesome but it's batch + enterprise only, so self-hosted users are kind of flying blind.

Had an idea for a new AgentFlow node, basically a quality gate you drop between your LLM and the next step. it scores the output and routes to a pass or fail port depending on whether it clears a threshold you set. wire fail back to the LLM node and you get self-correcting retry loops. scores land in $flow.state so downstream nodes can see them too.

For scoring, it'd support LLM-as-judge, exact match, regex, semantic similarity, and a custom JS function, same sandbox as the existing custom function node.
Before I start on a PR, wanted to make sure this isn't already on the internal roadmap somewhere. happy to reshape it however makes sense for the codebase 🙏