chore: scripts/ subdirectory reorganization (gates/, generators/, benchmarks/, ops/)

[mick-gsk]

Problem

142 scripts in a flat \scripts/\ directory make navigation difficult for both humans and agents.
While \make catalog --category \ now filters by category (added in this PR), the filesystem
still has no structural signal about which scripts belong to CI gates vs. benchmarks vs. ops.

Proposed Structure

\
scripts/
gates/ # 25 scripts: check_, validate_, gate.py
generators/ # 15 scripts: generate, sync_, integrate_
benchmarks/ # 27 scripts: benchmark_, ab_harness, mutation_
ops/ # 36 scripts: release, KPI, session, triage
analysis/ # 17 scripts: study_, *analysis, ablation
_experimental/ # 18 scripts: tmp*, trailers, demo GIFs
\\

Scope of Change

35 CI workflow YAMLs and ~24 Makefile targets reference scripts by path. All must be updated atomically with the file moves.

Required updates:

• 35 occurrences in .github/workflows/*.yml\
• ~24 \Makefile\ targets
• \scripts/catalog.py\ (SCRIPTS_DIR scan must recurse into subdirs via rglob)
• \AGENTS.md\ script path references
• \scripts/README.md\ tables

Implementation Notes

• Use \git mv\ to preserve history
• Verify with \make check\ + CI dry-run after move
• \check_agent_harness_contract.py\ may need path updates if it validates script existence

References

• Prerequisite: \catalog.py --category\ filter + \scripts/README.md\ (agent-facing index already added)
• \scripts/README.md\ Section 'Subdirectory Migration' documents this intent