refactor(ext/shared): typed StateHost + sweep as-any casts (Plan C Phase 1)

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>

extension/src/shared/popup-state.ts

@@ -20,7 +20,12 @@ export type View =
   | 'settings-vault'
   | 'trash'
   | 'devices'
-  | 'field-history';
+  | 'field-history'
+  // Vault-tab-only views; popup never navigates to these. Kept in the union so
+  // a single typed StateHost contract serves both surfaces (popup + vault).
+  | 'history'
+  | 'backup'
+  | 'import';
 
 export interface PopupState {
   view: View;
@@ -42,4 +47,11 @@ export interface PopupState {
   vaultSettings: VaultSettings | null;
   generatorDefaults: GeneratorRequest | null;
   historyItemId: ItemId | null;
+  // Vault-tab-only fields. The popup surface leaves these at their defaults
+  // (unlocked=false implicit via separate lock-screen view, drawer/panel false).
+  // Kept on the shared shape so VaultState satisfies StateHost.getState()
+  // without a cast.
+  unlocked?: boolean;
+  drawerOpen?: boolean;
+  typePanelOpen?: boolean;
 }