feat: unified Activity lane in Timeline with full-width layout

[fiddur]

Summary

Refactors the Timeline page to unify all activity types into a single lane with full-width responsive layout.

• Full-width layout: Uses ResizeObserver instead of fixed 1000px, fills the browser width
• Unified Activity lane: Sleep, exercise, meditation, nap, and duration tags (Sex, Sauna, YinYoga, Hot Bath, Breathwork, Holosync, Vocal Training, etc.) rendered in a single "Activity" lane — reduces from 4 tracks to 3 (Activity, Places, Tags)
• Source merging: When a duration tag (e.g., Holosync audio) overlaps >50% with a matching activity (e.g., Oura meditation), they merge into a single item with annotation — eliminates visual duplication
• Overlap detection: Real overlaps (e.g., Sex during sleep) use lane packing for sub-lanes, with visual indicators (reduced opacity, dashed yellow border) and a collapsible warning banner
• Point tag icons: Point tags render as stacked emoji/image icons from tag mappings (like DayView) instead of dashed vertical lines
• Tag icon support: Timeline now fetches fetchTagMappings to resolve emoji/image icons for tags

Data analysis (Feb 2026)

Found 37 duration tag instances; 6 overlapped with activities:

• 2x Sex during sleep (legitimate — user was awake within sleep session)
• 2x Holosync = meditation/nap (same activity, dual source → merged)
• 1x YinYoga = meditation (same activity, dual source → merged)
• 1x Hot Bath overlapping exercise by ~5min (timing imprecision)

Key implementation details

• TAG_ACTIVITY_MERGE_MAP defines tag→activity-type merge rules
• buildActivityLaneItems() orchestrates merging and overlap detection
• isDurationTagActivityLike() filters duration tags for the activity lane (excludes computer:*, lastfm sources)
• packLanes() utility handles non-overlapping lane assignment for both activities and point tags
• resolveTagIcon() shared helper for tag icon lookup

Not included

• DayView was not modified (could benefit from similar unification in the future)
• Pre-existing TypeScript errors in TagMappingsSettings.tsx (is_programmatic property) are unrelated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.81%. Comparing base (2c420cd) to head (575399d).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #288      +/-   ##
===========================================
+ Coverage    32.43%   32.81%   +0.38%     
===========================================
  Files          185      185              
  Lines        22651    22386     -265     
  Branches      1889     1889              
===========================================
  Hits          7346     7346              
+ Misses       15271    15006     -265     
  Partials        34       34              

Flag	Coverage Δ
backend	58.97% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.