Improve UI of pipelines and add branching logic

### Epic

_No response_

### Description

**As a Pipelines user**

**I want to see a more helpful visualization of pipelines**

**So that I can intuitively see what is pushed to the next stage, and what isn't**

A more effective visualization of pipeline stages would help users understand what is and isn't pushed to the next stage. Here is a nice example:
https://github.com/FlowFuse/flowfuse/issues/5429#issuecomment-3409796975

A customer has requested branching pipelines, where a pipeline could be set up that allows the user to move a particular subflow to another stage. That concept fits with this visualization.

###Requested By
https://app-eu1.hubspot.com/contacts/26586079/record/0-2/10735683795

### Which customers would this be available to

None

### Acceptance Criteria

- [ ] criteria 1
- [ ] criteria 2
- [ ] criteria 3
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### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate