Add Alt+Click link handoff with parent clip context

[XplosiveRaptor]

Summary

Adds a non-Reader link handoff flow to Web Clipper.

Users can now Alt+Click a hyperlink on a webpage to open it in a new tab with context preserved for Web Clipper. The destination clip can reference the source webpage, and if it exists, the note clipped from that original page.

Changes

• Added Alt+Click interception for eligible http/https links in the content script
• Opened handed-off links in a new active tab instead of replacing the source page
• Added per-tab handoff context storage in the background script
• Passed parent page context into popup extraction and template variable building
• Extended note-save/history handling to persist clipped note identity
• Added new template variables and updated template validation:
  • {{parentUrl}}
  • {{parentTitle}}
  • {{parentNoteName}}
  • {{parentNotePath}}
  • {{parentNoteLink}}