fix: include embedded context in view filters

[vycdev2]

Summary

• Include the visible context line in embedded-view filtering when todo.embedded.view.showContext is enabled.
• Preserve existing case-insensitive literal matching against todo lines and file paths.
• Add focused regression coverage and document the user-visible behavior in the unreleased changelog.

Verification

• npm install --no-audit --no-fund — passed; npm reported existing deprecation warnings.
• Focused embedded-filter regression test — passed.
• npm test — passed (137 tests).
• npm run compile — passed.
• npm run format:check — passed.
• git diff --check — passed.

Risk

• Low: filtering only gains the already-displayed context line as an additional match source; existing line/path matches are unchanged.

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