fix: sticky launch errors (#324)

This fixes an issue that there were sticky launch errors. When the
[following code
path](a15f0f301b/src/context.ts (L307-L339))
was throwing, the Error was stored in the Promise and not cleared
afterwards, this meant:

- If a browser was not there and the user tried to install it via
`browser_install` it was never working since the error was sticky.
- If other errors like CDP is not available yet etc. error appear a
re-connect would not work - the MCP server would require a restart.

Test plan: Since we don't have any `browser_install` tests I added a CDP
test for now to cover this bug.

tests/tabs.spec.ts

@@ -142,11 +142,11 @@ test('close tab', async ({ client }) => {
 });
 
 test('reuse first tab when navigating', async ({ startClient, cdpEndpoint }) => {
-  const browser = await chromium.connectOverCDP(cdpEndpoint);
+  const browser = await chromium.connectOverCDP(await cdpEndpoint());
   const [context] = browser.contexts();
   const pages = context.pages();
 
-  const client = await startClient({ args: [`--cdp-endpoint=${cdpEndpoint}`] });
+  const client = await startClient({ args: [`--cdp-endpoint=${await cdpEndpoint()}`] });
   await client.callTool({
     name: 'browser_navigate',
     arguments: {