feat(ground-study): own React request workspace (#4273)

[d-sorgcodexagent]

Summary

• lift one App-owned transactional workspace state for seeded regional-ground variation inputs
• make the Variation and Ground Surfaces panels controlled so complete user edits and exact import evidence survive mutually exclusive navigation
• expose a typed, UI-neutral snapshot/apply request port for the next contextual File-control slice
• refuse to compose disclosed illustrative regional defaults; invalid applies validate fully before a single reducer transition
• expose the supported restitution/rolling-resistance registry keys and fail closed visibly for the still-unimplemented browser ground executor
• update canonical handoffs, SPEC, and campaign manifest in the implementation commit

Verification

• full Rate React suite: 121 files / 763 tests
• independent focused rerun: 31 tests across reducer, App navigation, Variation, and Ground Surfaces
• TypeScript, zero-warning ESLint, and Rate Vite production build
• campaign manifest validator + 8 contract tests; docs, blocking-quality, module-size, and diff gates

Scope boundary

This is the workspace-ownership prerequisite only. It adds no file I/O, upload/download controls, PyQt behavior, or physics. The next child can bind the strict #4366 request contract without defaults, stale panel state, or an imperative component registry.

Refs #4273
Refs #4218
Refs #4267

[dieterolson]

Consolidated into #4409. Closing to reduce CI/CD runner load.