Phase 1: Contract spine — router, adapters, guardrails, slug, reset

[joshtvill]

Goal: each screen renders with zero side effects, using stable adapter APIs.

• Add services/sX_adapter.py for each screen.
• Refit screens to call adapters only.
• Remove disk writes from screens (route via services/artifacts.py).

[Fix: Navigation]

• Implement router in app.py.
• Screens return valid_to_proceed; nav lives only in app.py.
• Add ui.blocks.nav_back_next().

[Fix: Sidebar UI]

• Add dev-only sidebar in app.py behind env flag (DOE_WIZARD_DEBUG=1).
• No sidebar in prod.

[Fix: Service/adapter fixes]

• Put auto-slug in utils/naming.py + s1_adapter.
• Put roles candidates/validation in s3_adapter.

Acceptance

• app.py can walk S1→S6 without exceptions.
• No disk writes in screens.
• Dev sidebar toggles with env var.
• Grandfathered legacy screens exceptions in phase0 guardrails test gone
• legacy unit and e2e tests have xfail tags

[joshtvill]

additional changes:

• slug convention aligned to contract
• reset button added to all screens