Replaces the previously any-typed StateHost contract with a typed interface.
Adds double-registration guard and __resetHostForTests for vitest.
sendMessage wrapper is currently a pass-through; Phase 4 will fill its body
with the vault_locked intercept lifted from vault.ts.
Widens PopupState/View on shared/popup-state.ts to cover vault-tab-only
views (history, backup, import) and vault-tab-only fields (unlocked,
drawerOpen, typePanelOpen) so VaultState satisfies StateHost.getState()
without a cast. The popup surface ignores the new optional fields.
Drops the `any` annotations on vault.ts's registerHost callbacks now that
the typed StateHost contract infers them from PopupState.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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