Switch the assembly name to HellionChat so Dalamud uses
pluginConfigs/HellionChat for our config file and database
directory, instead of sharing those locations with the upstream
Chat 2 plugin. Code namespace stays ChatTwo.* so upstream
cherry-picks apply cleanly.
Rename the DalamudPackager manifest to HellionChat.yaml with
fork-specific name, author, repo URL, description, tags and
changelog. Plugin.PluginName becomes "Hellion Chat".
Add a one-shot migration in the plugin constructor that runs
before GetPluginConfig: if pluginConfigs/ChatTwo.json or the
ChatTwo/ directory exist and our equivalents don't, move them
into the HellionChat layout. Idempotent: only fires on the first
load where legacy paths are present and ours are not.
