Folder UX enhancement

Epic covering overall UX improvements for folder-related flows.

## Scope

### 1. Improve the folder creation modal

- The folder creation modal on the Data page behaves differently depending on the user role (regular user / project admin / admin).
- Re-adjust form item visibility and validation based on inter-field dependencies, including form item ordering.
- Consider all folder-creation entry points holistically: model card creation, deployment, session creation, etc.
- Improve feedback when folder creation fails.

### 2. Finish folder selection and sub-path components

- Improve the components for real-world use.
- Use a path picker for the sub-path input.

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Captured while working on branch: main

JIRA Issue: FR-3440

Trace the folder-creation entry points on the Data page, model card creation, deployment, and session creation, then inspect the folder creation modal and folder selection/sub-path components. Done means role-dependent visibility and validation are consistent, sub-paths use a path picker, and folder-creation failures provide better feedback.

Written by the indexing model from the issue text.