fix(compute): unify SSH Compute Skill materialization

[wen2zhou]

Problem

SSH Compute was materialized both as the bundled os-remote-compute-ssh Skill and as a bare remote-compute-ssh runtime document. The two documents could diverge, and generic Skill refreshes could overwrite the live host projection.

Proposed change

Use os-remote-compute-ssh/SKILL.md as the sole canonical document. Preserve its host projection during generic materialization, synchronize it before agent discovery and after Compute host mutations, and remove only the known bare legacy directory.

Scope and non-goals

This change only affects SSH Compute Skill provisioning. It does not alter Specialist switching, connector filtering, host persistence, SSH APIs, or Settings UI behavior.

Acceptance criteria and validation

• Bootstrap, generic refresh ordering, host create/delete, legacy cleanup, and filesystem discovery -> npm test -- src/main/compute/skill-provisioning.test.ts src/main/compute/skill-doc.test.ts src/main/skills/materializer.test.ts src/main/compute/ipc.test.ts src/main/settings/agent-runtime-manager.test.ts -> passed (80 tests).
• TypeScript validation -> npm run typecheck -> passed.
• Lint validation -> npm run lint -> passed.
• Full suite -> npm test -> attempted after the final material edit; blocked by the worktree/Vite filesystem restriction denying access to the parent-repository pdfjs-dist worker import. This fails unrelated renderer preview tests before they initialize.

Review focus

Please verify the canonical-path ownership boundary, preservation of dynamic host data across a bundled Skill refresh, and the narrow legacy-directory cleanup.