fix: shell quoting on playwright flags

[ferrandiaz]

Affected Components

• CLI
• Create CLI
• Test
• Docs
• Examples
• Other

Notes for the Reviewer

Fix shell argument quoting across CLI commands

Summary

• Add shared shell quoting utility (src/services/shell.ts)
• Fix argument quoting in pw-test, buildTestCommand, and package manager
• Remove duplicated quoting logic

Problem

Shell commands were constructed with inconsistent/incomplete quoting:

• pw-test only quoted args containing spaces, missing other metacharacters (|, $, ;, *, etc.)
• buildTestCommand had manual quoting that missed edge cases
• package-manager had a local unsafeQuoteArg function not shared elsewhere

Solution

Created a shared shell.ts utility with consistent quoting that handles all shell metacharacters. Safe characters (%+,-./:=@_ and alphanumeric) pass through unquoted; everything else gets properly escaped.