workspace: root-first tooling + benchmark artifact/reporting workflow

[0xpantera]

Summary

This PR consolidates the recent workspace/tooling migration and benchmark workflow improvements into a root-workspace-first flow.

1) Workspace-first docs/tooling execution

• Align docs build and benchmark commands to run from the root project (--project=.).
• Update docs CI workflow to instantiate workspace and build docs from root.
• Remove per-package/tool manifest drift from the committed state.

2) Benchmark artifacts and reporting

• Move benchmark outputs to run-scoped artifact directories:
  • benchmarks/artifacts/<run_id>/results/benchmark_results.json
  • benchmarks/artifacts/<run_id>/plots/*.png
  • benchmarks/artifacts/<run_id>/meta/run_meta.json
• Update benchmarks/run.jl and benchmarks/plot.jl to use the artifact structure.
• Add benchmarks/compare.jl for snapshot-to-snapshot diffs with thresholded regression reporting.
• Add benchmarks/report.jl orchestration:
  • run benchmarks
  • generate plots
  • compare latest vs latest-1
  • emit a markdown report with tables + comparison plots + run metadata

3) GrothExamples workflow update

• Finalize notebook-first direction for GrothExamples.
• Remove legacy script/test entrypoints that are no longer canonical.

4) BN254/proofs/docs alignment

• Apply BN254 field alias consistency updates across curves/proofs touched in this branch.
• Sync related README/Documenter/reference docs with the current workflow and naming.

Commits (grouped)

• workspace: align docs and docs CI to root project
• benchmarks: adopt artifact directories for results and plots
• examples: migrate to notebook-first workflow
• bn254: align field aliases across curves and proofs
• docs: sync references and remove legacy benchmark env snapshot

Notes

• Untracked local planning/review files were intentionally left out of commits.
• Benchmark report metadata is available for runs generated after metadata capture was added; older snapshots may show missing metadata fields.

Validation

• Root docs build command executes: julia --project=. docs/make.jl
• Benchmark plot/compare/report flows execute from root project (--project=.).