[P2] Respond to XTVERSION (CSI > 0 q) with terminal name/version

[benyblack]

Found in the AI harness readiness audit (docs/AI_HARNESS_READINESS_2026-08-01.md).

Some tools log terminal identity via XTVERSION. Respond DCS > | NovaTerminal <version> ST. Trivial once CSI dispatch distinguishes CSI > q from DECSCUSR (CSI Ps SP q, already guarded on intermediates at AnsiParser.cs ~line 938).

Add a parser unit test asserting the exact DCS reply and that DECSCUSR still works.