feat: add due date view

[vycdev2]

Summary

• add a Due activity-bar view that groups unfinished @due(...) tasks by local calendar date
• expand today by default, refresh on Todo edits, file changes, configuration changes, and midnight rollover
• support existing task actions in the Due view and reject impossible formatted due dates

Verification

• npm run compile — passed (webpack development build)
• npm test — passed (138 tests)
• npm run format:check — passed
• git diff --check — passed

Risk

• Medium: adds a new tree view and refresh paths, with extraction/date behavior covered by focused tests and the full suite.

Closes #68

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

[vycdev]

The Due view currently interprets examples inside inline code as live task metadata.

[vycdev]

Both this finished check and the @due(...) scan below operate on unmasked text. As a result, ☐ Explain \@done` @Due(2026-08-10)is wrongly omitted, while☐ Explain `@due(2026-08-10)`is wrongly added to the Due view. Please reuse the inline-code masking/status helper now ondevelop` before classifying the status and extracting due tags, with regressions for both cases.