Release v0.1.21

[marcelormendes]

Summary

• keep hidden Chat synchronized with Terminal activity and anchor Working timers at prompt submission
• settle stale Working/TODO/restart states and pin engine v0.8.5
• format elapsed time with S/M/H units
• highlight user messages in blue
• render GFM tables and retain local image thumbnails in conversation history
• bump Drover to v0.1.21

Verification

• npm run verify
• 64 test files / 565 tests passed
• isolated browser smoke for hidden Chat synchronization, TODO clearing, timers, tables, and image thumbnails