fix: adapt BootAgent to current DSH releases

[yujiezhang-ops]

Summary

• migrate DSH credentials to the current versioned version: 1 / refs document while preserving legacy entries
• probe both Chat Completions and Responses for DSH, prefer a working Responses route, and persist the selected protocol
• treat every HTTP 2xx provider probe as successful so UI status and message cannot contradict each other
• detect native Apple Silicon under Rosetta and prevent DSH/ZCode architecture mismatches
• use unique DMG mount points and always detach them after DSH Desktop installation

Real verification

Tested with isolated DSH_HOME directories using the official npm binaries:

• @deepseek-ai/dsh@0.1.5-rc.1 (latest)
• @deepseek-ai/dsh@0.1.5-rc.2 (next)

Both versions loaded the generated configuration and completed a real headless request through /v1/responses against a local protocol-compatible provider. The current Web profile also started successfully; its Models UI displayed the BootAgent-managed provider and recognized its credential.

No real external API key or user ~/.dsh data was used.

Validation

• go test ./...
• go vet ./...
• cd frontend && pnpm run typecheck
• cd frontend && pnpm run build
• task build:desktop
• launched bin/bootagent-desktop for a local smoke test
• git diff --check

Frontend Vitest currently reports 3 unrelated existing timing/render failures (App.test.tsx, AgentProfilePage.test.tsx, SettingsPage.test.tsx); 515 tests pass. This change does not modify frontend code.