Improve attribution accuracy and make hooks portable

[muraalee]

Attribution improvements:

• Parse Claude Code's structuredPatch for exact line numbers
• Read files for Cursor to derive line numbers from old_string location
• Add line context (before/after) for future disambiguation
• Remove substring/fuzzy matching to eliminate false positives
• Store sessionId and toolUseId for correlation

Portable hooks:

• Use agentblame command instead of hardcoded paths or bunx
• Git hooks now auto-update on agentblame init (removes old section)
• GitHub workflow uses npm-installed package instead of local source

Chrome extension:

• Improve pie chart color contrast (Blue, Red, Green, Purple order)
• Update logo with background color