fix: keep new tabs in tab_list even before URL is populated

[daidi]

Summary

• stop filtering out page/webview targets when target_info.url is empty
• apply this in both initial target discovery and runtime Target.targetCreated event handling

Why

When a page click opens a new tab, Chromium can emit the target before URL/title are populated.
If we drop empty-URL targets, tab may continue to report only one tab even though the browser switched to a new tab.

Regression source

This behavior appears to have been introduced by commit 8348b77 (fix: filter chrome:// internal targets from auto-connect discovery), which added !url.is_empty() filtering in target collection paths.
That change accidentally excluded valid newly-created tabs whose URL is not populated yet.

Repro

1. Open a page with <a target="_blank">
2. Trigger click via find text "..." click
3. Run tab

Before: sometimes only one tab is reported.
After: new tab is tracked immediately (may start with empty URL/title, later updated).

Validation

• cargo check in cli/ passes
• local manual repro confirms tab returns the second tab after new-tab click

[vercel]

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