fix: clean reminder duration separators

[vycdev2]

Summary

• remove conjunctions and punctuation that only separate reminder duration tokens
• preserve reminder prose that legitimately starts with "and"
• add regression coverage for documented multi-part duration examples and prose edge cases

Verification

• dotnet build — passed (0 errors; existing NU1903 warning for SQLitePCLRaw.lib.e_sqlite3 2.1.6)
• dotnet test --no-build --verbosity minimal — passed (234 tests)
• git diff --check — passed

Risk

• Low: the change is limited to extracting reminder text after the existing duration parser runs.

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