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/capacitor.settings.gradle

@@ -0,0 +1,3 @@
+// DO NOT EDIT THIS FILE! IT IS GENERATED EACH TIME "capacitor update" IS RUN
+include ':capacitor-android'
+project(':capacitor-android').projectDir = new File('../../node_modules/.bun/@capacitor+android@7.6.8+9556538e6e670b78/node_modules/@capacitor/android/capacitor')