docs(release): prepare Vibeshine 1.18.4-stable.3

Document the stable.2 hotfix delta so the release workflow publishes the intended user-facing fixes. Keep the notes limited to deployed stability and compatibility corrections.

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Model: GPT 5.6-Terra Max

Author: Nonary

release_notes/1.18.4-stable.3.md

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+# Vibeshine 1.18.4-stable.3 - 2026-08-18
+
+Notice: Vibeshine may trigger false-positive antivirus alerts. Details and workarounds are documented here: https://github.com/Nonary/vibeshine/issues/59
+
+## Fixes
+- Fixed unnecessary work on the v2 display-helper fast path and switching between helper engines.
+- Fixed virtual-display activation waiting on unstable monitor identity, recovery-state cleanup making the host unreachable, and stale portrait pointer rotation after restore.
+- Fixed Steam audio device ownership and restoration across app resumes and interrupted endpoint visibility changes.
+- Fixed Lossless Scaling launcher selection so a game path cannot be launched as the scaling tool.
+- Defaulted AMD encoding to the supported FFmpeg AMF path while keeping native AMF as an explicit experimental option.
+- Fixed configured RTSS frame limiting being ignored for virtual displays unless it is explicitly enabled.