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/Plugin.cs

@@ -189,8 +189,8 @@ public sealed class Plugin : IAsyncDalamudPlugin
         if (Config.Version < 16)
         {
             throw new InvalidOperationException(
-                $"HellionChat v1.4.7 requires config schema v16, got v{Config.Version}. "
-                    + "Please install v1.4.2 first to migrate the configuration, then upgrade to v1.4.7."
+                $"HellionChat v1.4.8 requires config schema v16, got v{Config.Version}. "
+                    + "Please install v1.4.2 first to migrate the configuration, then upgrade to v1.4.8."
             );
         }
         Config.Version = 17;