feat(ext/sw): parse + commit handlers for LastPass import

parse_lastpass_csv is a pure pass-through to the WASM bridge.
import_lastpass_commit re-mints each item's ID via
state.wasm.new_item_id() (same pattern as add_item), encrypts
and writes per-item via git.writeFile, then writes the manifest
last. Per-item commits + a final manifest commit — extension
GitHost has no atomic-batch API, so the single-commit semantics
the CLI provides aren't replicable here.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

extension/src/service-worker/router/popup-only.ts

@@ -507,6 +507,52 @@ export async function handle(
         return { ok: false, error: (e as Error).message };
       }
     }
+
+    case 'parse_lastpass_csv': {
+      try {
+        const json: string = state.wasm.parse_lastpass_csv_json(new Uint8Array(msg.bytes));
+        const parsed = JSON.parse(json) as {
+          items: Item[];
+          warnings: Array<{ row: number; title?: string; message: string }>;
+        };
+        return { ok: true, data: parsed };
+      } catch (e) {
+        return { ok: false, error: (e as Error).message };
+      }
+    }
+
+    case 'import_lastpass_commit': {
+      const handle = session.getCurrent();
+      if (!handle || !state.gitHost || !state.manifest) return { ok: false, error: 'vault_locked' };
+      if (msg.items.length === 0) return { ok: false, error: 'no items to import' };
+
+      try {
+        const total = msg.items.length;
+        for (let i = 0; i < msg.items.length; i++) {
+          const item = msg.items[i];
+          // Items arrive with IDs already minted by the WASM bridge. We
+          // overwrite that with a fresh extension-generated ID so the SW
+          // remains the single ID-issuance authority for new items in the
+          // remote — same pattern as `add_item`.
+          const id = state.wasm.new_item_id();
+          const reIdItem: Item = { ...item, id };
+
+          await vault.encryptAndWriteItem(
+            state.gitHost, handle, id, reIdItem,
+            `import: ${reIdItem.title} (${i + 1}/${total})`,
+          );
+          state.manifest.items[id] = itemToManifestEntry(reIdItem);
+        }
+
+        await vault.encryptAndWriteManifest(
+          state.gitHost, handle, state.manifest,
+          `manifest: import ${total} items from LastPass`,
+        );
+        return { ok: true, data: { summary: { itemCount: total } } };
+      } catch (e) {
+        return { ok: false, error: (e as Error).message };
+      }
+    }
   }
 }