Replace service-definition.toml with deployment-config.yaml

Replace all references to `service-definition.toml` with `deployment-config.yaml` (YAML format) across the frontend codebase.

## Files Affected

- `react/src/hooks/useModelServiceLauncher.ts` — file existence check and download/parse logic (TOML → YAML parser)
- `react/src/components/LegacyModelTryContentButton.tsx` — file existence check
- `react/src/components/VFolderTextFileEditorModal.tsx` — schema mapping entry (type: toml → yaml)

## Changes

- Check for `deployment-config.yaml` instead of `service-definition.toml`
- Replace `smol-toml` parser with `yaml` parser
- Update `VFolderTextFileEditorModal` schema mapping to yaml type (no schema file yet)

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Captured while working on branch: 04-16-feat_fr-2591_replace_vfolder_yaml_parsing_with_graphql_query

JIRA Issue: FR-2592