feat: Timeline UI Enhancements and Issue Tracking

[archdex-art]

UI and Analytical Refinements for the Timeline Engine

• Issues Shift Diffing: Ad-Hoc comparisons now render a comprehensive list of exactly which architectural and code-quality issues were Introduced and Resolved between two commits.
• Snapshot Issues List: The main timeline view now displays a scrollable list of all active issues present at the exact moment of the selected historical commit.
• Git Diff Colorization: The raw file diff modal now features line-by-line syntax highlighting (green for additions, red for deletions, cyan for chunks), perfectly mirroring IDE implementations.
• Explorer View Upgrades: The changed files list now separates filenames (main header) from directory paths (subtext) for a much cleaner scanning experience.
• Tooltips: Added informative hover tooltips via (i) icons to explain complex metrics like Arch Score and Coupling to end-users.
• Git Integration Improvements: Backed the timeline endpoints with direct git diff --name-status and physical temp-file .tar extraction to eliminate Node.js memory buffer limits on massive repositories.