Include start node when pulling workflows, plus options refactor

[josephjclark]

Third attempt to set a start key on workflows when loading from app state.

Fixes #1213 I think
Fixes #1204

This turns out to be quite a big deal because basically the handling of start and options just isn't so good.

So changes in this PR:

• The workflow.json format of { workflow, options } is now considered old hat and legacy
• Now a workflow.yaml or workflow.json just contains the workflow. No option stuff.
• A workflow supports a start key as first class citizen
• When pulling from app state, we set this start key to the trigger (hard coded)
• Project.yaml and workflow.yaml now have a consistent structure (including options, which I think is never used)

AI Usage

Please disclose how you've used AI in this work (it's cool, we just want to know!):

• Code generation (copilot but not intellisense)
• Learning or fact checking
• Strategy / design
• Optimisation / refactoring
• Translation / spellchecking / doc gen
• Other
• I have not used AI

You can read more details in our Responsible AI Policy

Release branch checklist

Delete this section if this is not a release PR.

If this IS a release branch:

• Run pnpm changeset version from root to bump versions
• Run pnpm install
• Commit the new version numbers
• Run pnpm changeset tag to generate tags
• Push tags git push --tags

Tags may need updating if commits come in after the tags are first generated.

[josephjclark]

Wow I thought this was going to take ages - but I think this is it!

I want to run some manual QA tomorrow with openfnx:

• Run a { workflow, options } from a workflow.json
• Run a { workflow, options } from a workflow.yaml
• Run a (workflow) from a workflow.json
• Run a (workflow) from a workflow.yaml
• Respect options.start when it's provided
• Fetch from the app and run the project: it should start from the correct node

I'll also check what integration tests are like for this stuff

EDIT: I have integration tests for most of this, just a couple of manual tests and we good