chore: add rSHUD submodule + OpenSpec change

[DankerMu]

Summary

• Add rSHUD/ as a submodule (fork: DankerMu/rSHUD)
• Land OpenSpec change refactor-r-spatial-stack-sf-terra
• Update root submodule workflow notes

Spec / proposal

• OpenSpec change id: refactor-r-spatial-stack-sf-terra

Testing

• openspec validate refactor-r-spatial-stack-sf-terra --strict --no-interactive

Closes #19

[DankerMu]

Review: spec-driven-workflow

• Scope: Small and matches [SHUD-NC] 以 submodule 管理 rSHUD + 落地 OpenSpec 提案 #19 (submodule wiring + OpenSpec change landing).
• Spec/contract:
  • OpenSpec change refactor-r-spatial-stack-sf-terra is present and validates.
• Repo hygiene:
  • .gitmodules correctly points rSHUD to the fork.
  • Root AGENTS.md documents the 3-submodule workflow clearly.
• CI: OpenSpec + Python smoke are green.

[DankerMu]

Review: spec-driven-workflow (via codeagent)

Review Summary

• Submodule wiring looks correct: rSHUD is added in .gitmodules and as a gitlink (no extra behavior changes beyond introducing the submodule).
• Root docs are updated appropriately for the third submodule and workflow (AGENTS.md).
• OpenSpec change is well-formed: proposal + tasks + (optional) design + delta spec are present, and openspec validate refactor-r-spatial-stack-sf-terra --strict passes.

Issues Found

• [MAJOR] OpenSpec approval gate ambiguity: this PR contains both the proposal and an implementation step (“Repo wiring” is already done, but still unchecked in openspec/changes/refactor-r-spatial-stack-sf-terra/tasks.md). Either split into (A) proposal-only PR then (B) implementation PR after approval, or explicitly treat this PR as the approval PR and update the “Repo wiring” tasks accordingly.
• [MINOR] Follow-up hygiene: tasks propose installing into .Rlib/, but .Rlib/ is not ignored in .gitignore yet; add it before any local-R-lib install work lands to avoid accidental commits.
• [NIT] CI doesn’t checkout submodules (fine for current jobs). If future CI touches rSHUD/ or other submodules, set actions/checkout to fetch submodules.

Decision
PASS — score 4/5.