fix: preserve RSS query commas

[vycdev2]

Summary

• preserve commas inside RSS feed query values instead of treating them as display-name separators
• keep whitespace-, comma-, and semicolon-separated bulk URL input working
• add regression coverage for single-feed, multiline, and bulk input forms

Verification

• dotnet build — passed with 0 errors; existing NU1903 advisory warning remains for SQLitePCLRaw.lib.e_sqlite3 2.1.6
• dotnet test --no-build — passed, 234 tests
• git diff --check upstream/develop...HEAD — passed

Risk

• Low: the change is isolated to RSS subscription input tokenization and is covered by focused parser tests.

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