Add bounded semantic requirement workspace

[iperev]

Summary

• add canonical context compose/slice, semantic diff, and traceability graph commands
• add a loopback-only requirement workspace with source-bound question handoffs, paginated views, and one-shot terminal sessions
• add compact JSON process output and publish CLI contract v2
• add pinned cross-browser runtime proof, independent proof admission, and required CI/release gates

Verification

• npm run check
• go test -race ./internal/command/requirementbrowser ./internal/command/requirementcontext ./internal/command/requirementdiff ./internal/command/requirementgraph -count=1
• terminal and lifecycle falsifiers repeated with -count=20
• two concurrent npm run browser:check runs, each 6/6 across Chromium, Firefox, and WebKit
• git diff --check

Non-claims

This PR does not prove provider CI completion, registry publication, rollout, or production readiness.