fix(onboarding): backport BYOK completion persistence to v1.1.2

[syzsunshine219]

Summary

• Backport fix(onboarding): prevent replay after switching to BYOK #343 onto release/v1.1.2.
• Preserve completed onboarding state when a signed-in account switches to local BYOK/API-key mode, preventing the first-encounter report from loading again.
• Keep firstEncounterReportStatus installation-scoped; a genuinely pending report still follows the normal onboarding route.
• Keep the fix on main; the release workflow uses the main merge as the canonical backport source.

Backport provenance

• Main merge: e679cf9caff48c59f03bb5587d35152cde013988
• Implementation source: a4531a04f76b8767d57c19e83b8919e865b2fe39
• Release commit: 7580586ac6a64d45e8d7984ea1839f9e11f95818
• Commit trailer: Backport-of: e679cf9caff48c59f03bb5587d35152cde013988

Verification

• Node 22 targeted regressions: 4 files, 120 tests passed.
• Project Harness Full: all 12 product evidence commands passed, including lint, affected typecheck/workspace tests, Local API matrix, desktop UI assertions, critical smoke, full build, distribution boundary, and diff sanity.
• Harness reports verificationPassed: true. Its delivery gate remains base_not_ancestor because the current Harness binding has immutable base upstream/main, while this PR intentionally targets release/v1.1.2.
• Unsigned v1.1.2 package manual verification remains pending.