fix: Replace remaining agent.open() calls in voice and cache tests

Fixed agent.open() in:
- tests/magnitude/09-voice.mag.ts (4 instances)
- tests/magnitude/cache-success.mag.ts (1 instance)

All Magnitude tests now use the correct agent.act('Navigate to...') API.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/magnitude/09-voice.mag.ts

@@ -2,7 +2,7 @@ import { test } from 'magnitude-test';
 
 test('[Happy Path] User can have a full voice conversation with AI', async (agent) => {
   // Act: Navigate to chat page (assumes user is already authenticated)
-  await agent.open('http://localhost:3000/chat');
+  await agent.act('Navigate to http://localhost:3000/chat');
 
   // Check: Initial state - voice button shows "Start Voice Conversation"
   await agent.check('A button with text "Start Voice Conversation" is visible');
@@ -76,7 +76,7 @@ test('[Happy Path] User can have a full voice conversation with AI', async (agen
 });
 
 test('[Unhappy Path] Voice mode handles errors gracefully', async (agent) => {
-  await agent.open('http://localhost:3000/chat');
+  await agent.act('Navigate to http://localhost:3000/chat');
 
   // Act: Start voice mode
   await agent.act('Click the "Start Voice Conversation" button');
@@ -93,7 +93,7 @@ test('[Unhappy Path] Voice mode handles errors gracefully', async (agent) => {
 });
 
 test('[Happy Path] Text input is disabled during voice mode', async (agent) => {
-  await agent.open('http://localhost:3000/chat');
+  await agent.act('Navigate to http://localhost:3000/chat');
 
   // Check: Text input is enabled initially
   await agent.check('The text input field "Or type your thoughts here..." is enabled');
@@ -112,7 +112,7 @@ test('[Happy Path] Text input is disabled during voice mode', async (agent) => {
 });
 
 test('[Happy Path] User can type a message while voice mode is idle', async (agent) => {
-  await agent.open('http://localhost:3000/chat');
+  await agent.act('Navigate to http://localhost:3000/chat');
 
   // Act: Type a message in the text input
   await agent.act('Type "This is a text message" into the text input field');

tests/magnitude/cache-success.mag.ts

@@ -8,7 +8,7 @@
 import { test } from 'magnitude-test';
 
 test('Node publishes successfully with cache (no warnings)', async (agent) => {
-  await agent.open('http://localhost:3000');
+  await agent.act('Navigate to http://localhost:3000');
 
   // Login
   await agent.act('Click the "Log in with Bluesky" button');