chore: sort progress entries chronologically

[bluelephant825]

Summary

• reorder every dated PROGRESS.md entry from oldest to newest
• treat adjacent dated lines as separate entries even when historical blank separators are missing
• preserve stable ordering for entries sharing the same date
• establish a clean changelog base before the remaining work from Browse & Canvas, browser extensions, Ollama runtimes, and header focus mode #96 is proposed as focused pull requests

Test plan

• Verify every dated entry start is non-decreasing
• Verify all original entry payload hashes are preserved
• Verify exactly one blank line separates entries
• Verify git diff --check passes
• Verify the branch changes only PROGRESS.md

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