Add timeline branching toggle to settings

[vincentmakes]

Summary

This PR adds a new "Timeline: Branching" toggle to the Settings > Advanced section, allowing users to disable the branch visualization for overlapping experiences and render a flat timeline instead.

Key Changes

• Settings UI: Added new toggle switch in public/index.html for timeline branching control (enabled by default)
• Admin Panel: Updated public/shared/admin.js to load and save the timeline branching setting via API
• Timeline Rendering: Modified public/shared/scripts.js to conditionally apply branch computation based on the setting:
  • When enabled (default): Uses existing computeTimelineBranches() for branched visualization
  • When disabled: Renders a flat timeline with all items on track 0
• Internationalization: Added translation strings for the new setting in 8 languages (EN, DE, ES, FR, IT, NL, PT, ZH)
• Version Bump: Updated to v1.13.0 and added changelog entry

Implementation Details

• The timelineBranching global variable defaults to true to maintain backward compatibility
• The setting is loaded from the API with a fallback default of true
• When branching is disabled, timeline segments are created with track: 0 and branchGroup: null, resulting in a linear layout
• The feature integrates seamlessly with existing timeline rendering logic without breaking changes

https://claude.ai/code/session_019Tpjg627uvP5Rqeh9jbyEU