Add progress bar for batch processing

[ahmed-sekka]

Description

Currently, batch processing shows minimal progress feedback. Add a rich progress bar with file count and ETA.

Expected behavior

Processing documents ━━━━━━━━━━━━━━━━━━━━ 45/100 files • 00:02:30 remaining
  Current: invoice_2024.pdf

Files to modify

• src/core/cli/commands/batch.py

Resources

• Rich library (already a dependency): https://rich.readthedocs.io/en/latest/progress.html

Acceptance criteria

• Show progress bar with percentage
• Display current file being processed
• Show ETA based on average processing time
• Handle errors gracefully without breaking progress display