Flatten repo: move client/ contents to repo root

The project is no longer a monorepo/workspace - there is only a single
app package. Remove the redundant client/ nesting: all source, the
Capacitor Android project, config files and package.json/tsconfig now
live directly at the repo root.

- Merge client/package.json into root package.json (drop the
  workspaces field and the now-unnecessary bun --cwd client wrappers).
- Merge client/bun.lock (the actual dependency lockfile) into the
  root, replacing the stale workspace-only root lockfile.
- Move src/, public/, android/, index.html, vite.config.ts,
  capacitor.config.ts, tsconfig.{app,node}.json to the repo root.
- Update Dockerfile.android to build from the repo root instead of
  cd'ing into client/.
- Update .github/workflows/ci.yml type-check step to run bun run build
  directly instead of bun --cwd client run build.
- Update README.md and .github/copilot-instructions.md to drop
  references to the client/ subdirectory.
- Drop the stale server/downloads/ entry from .gitignore (leftover
  from an old server-based architecture that no longer exists).

android/app/src/main/res/layout/activity_main.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    tools:context=".MainActivity">
+
+    <WebView
+        android:layout_width="match_parent"
+        android:layout_height="match_parent" />
+</androidx.coordinatorlayout.widget.CoordinatorLayout>