fix: harden release readiness and user workflows

[D-sudoasd]

Summary

• fail closed on missing/unknown structured Q units, support standards-compliant reciprocal metres, preserve text compatibility, and harden YAML/empty-array/XML-write boundaries
• make Workbench preflight content-aware without blocking disabled optional inputs; preserve approvals across language-only refreshes and localize lifecycle/completion feedback
• clarify development-vs-stable installation, BL19B2 dry-run operation, scientific acceptance limits, and JOSS/release-readiness status

Verification

• Python 3.11: 1155 passed with -W error
• Python 3.12: 1155 passed with -W error
• independent re-review: APPROVE; 649 focused tests passed
• Ruff and git diff --check: passed
• clean external clone: sdist/wheel build, fresh wheel [gui,hdf5] install, CLI/import/pip check, and synthetic minimal-2D smoke passed

Boundaries

This is engineering release-readiness, not measured BL19B2 scientific acceptance. The 2.0.0 source candidate remains unreleased; author metadata, research-use evidence, and measured-beamline acceptance remain explicit submission gates.