fix(cli): handle empty --browserUrl to prevent Invalid URL crash

[yasirusman85]

This PR fixes a startup bug in chrome-devtools-mcp where passing --browserUrl "" (as happens in VS Code Insiders with GitHub Copilot MCP integration) caused the process to exit with:

Invalid URL

Before fix

node build/src/index.js --browserUrl ""
# → Invalid URL, process exited with code 1

After fix

node build/src/index.js --browserUrl ""
# → Falls back to channel=stable, server starts successfully
chrome-devtools-mcp exposes content of the browser instance...

Root cause

• cli.ts coerced even empty strings via new URL(url), which throws.
• VS Code Insiders MCP integration sometimes passes --browserUrl "" instead of omitting the flag.

Fix

• Updated coerce in cli.ts to safely ignore empty/blank strings.
• Fallback logic now correctly assigns channel: "stable".

Impact

• Fixes MCP server crash in VS Code Insiders.
• Preserves existing behavior for valid URLs and other CLI options.

[Lightning00Blade]

@yasirusman85
Please remove all unrelated changes to the console, and after that I will be happy to review the PR.