Rename remaining HDF5 groups to CamelCase + add CLAUDE.md naming convention #226

Context

PR #225 restructured the edge_scan/ and vacuum/ groups of gpec.h5 into the new CamelCase schema:

• edge_scan/* → EdgeScan/* (power-norm default) and EdgeScan/XiNorm/* (ξ-space for benchmarking)
• vacuum/ split into FreeBoundaryStability/ (energy matrices + eigenmode energies) and SurfaceGeometries/{Plasma,Wall}/{x,y,z}

The remaining top-level groups are still lowercase/abbreviated. They should be renamed for a consistent CamelCase schema.

Proposed renames

Already migrated (no change needed here): EdgeScan/, FreeBoundaryStability/, SurfaceGeometries/.

Scope of work

1. Update the writer in src/GeneralizedPerturbedEquilibrium.jl to emit the new group names.
2. Update every reader:
   • src/Analysis/ForceFreeStates.jl (stability plots)
   • src/Analysis/* (other analysis modules)
   • benchmarks/*.jl
   • test/runtests_fullruns.jl
   • regression-harness/cases/*.toml
   • scripts/*.jl
3. Rebaseline any hard-coded numerical expectations if they were tied to old paths.
4. Add a new "HDF5 naming conventions" section to CLAUDE.md so future Claude Code sessions emit consistent CamelCase group names from the start. Recommended content:
   • Top-level groups: CamelCase singular or plural noun (e.g. FreeBoundaryStability, SingularSurfaces)
   • Field names: snake_case (e.g. total_energy, eigenmode_energies)
   • Reserved subgroup names: XiNorm/ for ξ-space counterparts of Φ-space (power-norm) defaults
   • Physical point clouds live under SurfaceGeometries/<SurfaceName>/{x,y,z}
5. Regenerate regression baselines on develop after the merge.

Why

The mixed schema (EdgeScan/ next to equil/ and integration/) is confusing for anyone inspecting gpec.h5. Tackling the remaining groups in a single focused PR keeps the migration easy to review and limits the blast radius of downstream tool breakage.

The CLAUDE.md addition is the key follow-up — without a codified convention, these renames will drift again the next time a new group is added.