Add appearance settings and fix release versions

[itsmeares]

Summary

• add administrator-managed JellyChat colors and server-wide custom CSS
• add compact anchored HSV/alpha picker while preserving advanced CSS color fields
• clear stale hex validation when picker controls generate a valid value
• preserve outside-click focus and limit swatch focus restoration to explicit dismissal
• keep GitHub tags/assets three-part while Jellyfin metadata remains four-part

Why

JellyChat previously kept its default styling when Jellyfin used custom branding. Final picker testing also exposed stale validity and focus regressions, while release automation conflated GitHub release versions with Jellyfin plugin versions.

Impact

Administrators can align JellyChat with Jellyfin branding from the existing plugin configuration page. Picker drafts still apply only through Apply. Release tags and assets use MAJOR.MINOR.PATCH; plugin, assembly, build.yaml, and manifest metadata use MAJOR.MINOR.PATCH.0. Existing APIs, plugin identity, injection architecture, room behavior, and client drawer opacity remain unchanged.

Validation

• dotnet test Jellyfin.Plugin.JellyChat.sln -c Release — 24 passed
• dotnet publish Jellyfin.Plugin.JellyChat/Jellyfin.Plugin.JellyChat.csproj -c Release
• inline configuration JavaScript syntax checks
• release version mapping checks for v1.2.0 → 1.2.0 / 1.2.0.0
• git diff --check