chore: bump version to 1.4.8, sync manifest

- csproj <Version>, Plugin.cs schema-gate self-reference, repo.json
  (AssemblyVersion, TestingAssemblyVersion, 3x DownloadLink URLs).
- README.md shield badge, version header, Project Status body.
- docs/CHANGELOG.md gains a v1.4.8 section above v1.4.7.
- docs/ROADMAP.md flips Next Cycle to v1.4.9 (Plugin-Load Render
  Polish), v1.4.8 moves into the released history above v1.4.7.
- Config schema stays at v17, Migration v17 stays additive.

repo.json Changelog field and HellionChat.yaml changelog block plus
the new forge-posts/v1.4.8.md follow in a separate commit (slim-drop
of v1.4.4 happens there).

HellionChat/HellionChat.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Dalamud.NET.Sdk/15.0.0">
     <PropertyGroup>
         <!-- Independent versioning; see yaml changelog for upstream Chat 2 base -->
-        <Version>1.4.7</Version>
+        <Version>1.4.8</Version>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
         <!-- Use lock file to pin exact versions -->