Summary

• Adds typed Deck-side preview data for launch and stream intent state.
• Exposes public-safe launch/stream preview copy in the Deck shell while keeping the CTA inert.
• Adds behavior coverage for preview-only safety and copy-only URI behavior.

Scope / non-goals

This is a preview/data-contract slice only. It does not add live streaming or execution behavior.

This PR does not:

• invoke Moonlight or Sunshine;
• launch games or processes;
• call Polaris live launch/session endpoints;
• add network discovery or pairing;
• persist HostStore, credentials, certificates, or keys;
• add native stream runtime/decoder/input/session code;
• perform Steam Deck runtime smoke coverage.

Validation

• git diff --check origin/master...HEAD -- clients/deck
• cmake -S clients/deck -B build/deck-fallback-smoke -DNOVA_DECK_BUILD_QT_SHELL=OFF -DCMAKE_BUILD_TYPE=Debug
• cmake --build build/deck-fallback-smoke
• ctest --test-dir build/deck-fallback-smoke --output-on-failure
• cmake -S clients/deck -B build/deck-qt-smoke -DNOVA_DECK_BUILD_QT_SHELL=ON -DCMAKE_BUILD_TYPE=Debug
• cmake --build build/deck-qt-smoke
• ctest --test-dir build/deck-qt-smoke --output-on-failure
• Public-surface and forbidden-primitive scans over the Deck diff.