feat: add threshold control UI and batch scan (Level 3)

[ayushlad9108]

Part 1 - Threshold Control UI:

• Add adjustable gap threshold slider (5s to 3600s) in Evidence Ingestion card
• Display active threshold value dynamically with smart formatting (s/m/h)
• Persist threshold preference in localStorage across sessions
• Wire threshold to /analyze API call (replaces hardcoded 60s)

Part 2 - Batch Scan:

• Update file input to accept multiple files
• Queue and run sequential /analyze calls per file
• Aggregate results into combined KPI cards (avg score, total gaps)
• Show per-file summary cards in Registry tab (Batch Analysis Summary)
• Add File Source column to incident registry table
• Update search/filter/sort to work across all files
• Batch-aware JSON and CSV export formats

Backend:

• /analyze now returns metadata (filename, threshold_used, analyzed_at)

Test data:

• Add test_logs/auth.log, syslog.log, access.log for local testing

[sutanjoyb]

Fix the conflicts!! @ayushlad9108

[sutanjoyb]

@ayushlad9108 Is there any updates??