fix: preserve punctuation when removing completion tags

[vycdev2]

Summary

• Keep punctuation immediately before @done, @cancelled, @lasted, or @wasted when reopening a task; continue consuming whitespace separators.
• Add a regression test and an unreleased changelog entry.

Verification

• Regression reproduced on unchanged implementation: 415 passing, 1 failing.
• npm run check — passed: typecheck, 416 tests, webpack compile, and formatting.
• git diff upstream/develop...HEAD --check — passed.

Risk

• Low: change is confined to removal of completion and elapsed-time tags, preserving non-whitespace tag boundaries.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.