Summary

Fix wrong outline selection at heading boundaries in Markdown files.

When clicking headings in the Outline Panel for Markdown, the selected item showed as N-1 (previous heading) instead of N. Root cause: the outline_location() function's sort key prioritized depth over cursor position, causing deeper sections to win even when the cursor was at the exact start of a shallower section.

Fixes #52418

How to Review

• outline_panel.rs:3395 : Sort key change adding cursor_past_start as primary criterion
• outline_panel.rs:8094 : New comprehensive test with 8 boundary/nesting cases

Self-Review Checklist

• Reviewed diff for quality and correctness
• Tests cover the new/changed behavior (8 test cases added)
• No unsafe code changes
• All 12 tests pass (11 existing + 1 new)

Video

Release Notes:

• Fixed Outline Panel selection being off-by-one at Markdown heading boundaries