Relocate app data and package build output

Adds a new `AppPaths` helper and moves runtime/user-generated files (`init.config`, `custom_set.txt`, cache, WebView2 data) into `%LocalAppData%\Lithium` with readable fallback to portable files. WebView2 initialization now sets a loader DLL path, uses an explicit user data folder, and surfaces runtime-missing errors.

The build/publish pipeline is updated to emit a clean `Build\` layout with dependencies under `lib\`, remove duplicate root DLL/docs, and align probing/runtime settings for net48 x64 output. Supporting updates include ignore rules for build/runtime artifacts, refreshed agent build/release docs, and endpoint URL/domain updates.

.gitignore

@@ -17,6 +17,9 @@
 mono_crash.*
 
 # Build results
+[Bb]in/
+[Oo]bj/
+[Bb]uild/
 [Dd]ebug/
 [Dd]ebugPublic/
 [Rr]elease/
@@ -228,6 +231,17 @@ _pkginfo.txt
 # but keep track of directories ending in .cache
 !?*.[Cc]ache/
 
+# Runtime-generated application data
+*.exe.WebView2/
+
+# Local release archives
+*.7z
+*.zip
+
+# Local Claude Code and VS Code settings
+.claude/
+.vscode/
+
 # Others
 ClientBin/
 ~$*