Run note-recovery primitives on the switch-guardian path

[haseebrabbani]

Sub-issue of #357. Follow-up: depends on the three SDK recovery primitives (transport drain, proposal-note import, public backfill).

Context

Switching Guardian operators loses the same local note context as device-loss recovery: the switch path performs a chain sync and re-registers state on the new Guardian, but carries no note or history context. Any note-recovery capability built for #357 should be exercised (or explicitly scoped out) on the switch path too.

Scope

• Invoke the transport backlog drain and public-note backfill on the switch-guardian flow where they apply; include proposal-embedded note import if pending proposals survive the switch.
• If any primitive is deliberately skipped on this path, document why.

Acceptance criteria

• Switch flow either runs the applicable recovery primitives or documents the decision not to.
• A test covering note continuity across a guardian switch (note received before switch remains consumable after).

Low urgency; small once the primitives exist.