Issue: Implement Progress Feedback for Large Result ZIP Generation

[chraibi]

Description

Generating simulation result ZIP files—especially for large-scale simulations or multi-run ensembles—can lead to significant latency. Currently, the UI provides no feedback during the "Packaging" phase, leading to a poor user experience where the app appears unresponsive while waiting for the download to trigger.

Current Behavior

• When requesting a results download, the UI remains static until the browser's download prompt appears.
• For large datasets, this "silent period" can last several seconds or minutes.

Expected Behavior

• Display a Progress Bar or Status Indicator immediately upon clicking the download/generate button.
• Provide real-time (or simulated) feedback indicating the compression progress.
• The indicator should dismiss automatically once the file transfer begins.

Technical Requirements

• State Management:

• Add an isGeneratingArchive boolean to the UI state.

• Track downloadProgress as a percentage (0–100).

• UI Component:

• Integrate a progress bar into the Simulation Panel or as a global toast/overlay.

• Ensure the "Download" button is disabled during this process to prevent multiple redundant requests.