feat: add URL-based browser configuration

[vinceyyy]

Fixes #229

Summary

• Add open.browser and open.<url>.browser git config support, allowing different browsers for different URL patterns (e.g., Edge for work repos, Safari for personal)
• Use eval for the browser command to properly handle quoted arguments like open -a 'Microsoft Edge'
• Reuses the existing getConfig / --get-urlmatch mechanism — only 3 lines added to the script

Example URLs being parsed

# With: git config "open.https://github.com/company-org.browser" "open -a 'Microsoft Edge'"
# Repo: git@github.com:company-org/repo.git
# Opens in: Microsoft Edge

# With: git config open.browser "open -a Safari"
# Repo: git@github.com:personal/repo.git
# Opens in: Safari (default fallback)

Test plan

• Default browser via open.browser config
• URL-specific browser via open.<url>.browser config
• URL-specific config overrides default config
• Non-matching URL falls back to default browser config
• Quoted arguments in browser command (e.g., 'Microsoft Edge')
• BROWSER env var still takes priority over all config
• All 73 existing + new tests pass