Revamp Digital Forge benchmark dashboard and README

[MohammedPathariya]

Summary

• add guarded benchmark checkpointing and active benchmark reports
• update benchmark dashboard ordering and report selection UI
• document the current Digital Forge architecture, setup, benchmark evidence, and limits in the README

Verification

• .venv/bin/python -m pytest tests/test_benchmarks.py tests/test_baseline.py tests/test_digital_forge_benchmark.py -q
• .venv/bin/python -m ruff check backend benchmark tests
• npm run lint
• npm run typecheck
• git diff --check