Present local device sign-in and plaintext consent

Assistant-model: GPT-6 Sol
Assistant-workflow: local-device-auth (run cc80c691-7450-4025-bf56-613bc047c5b7)
Assistant-verification: Playwright E2E passed: focused local device flow with away-page approval and return navigation, 1/1 after prior red failure
Assistant-verification: Bun typecheck passed: mise exec -- bun run types (all workspaces and E2E)
Assistant-verification: Bun lint passed: mise exec -- bun run ci (dprint, oxlint, token checks)
Co-authored-by: Alex Lavaee <lavaman131@github.com>