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).

tsconfig.json

@@ -1,30 +1,7 @@
 {
-  "compilerOptions": {
-    // Environment setup & latest features
-    "lib": ["ESNext"],
-    "target": "ESNext",
-    "module": "Preserve",
-    "moduleDetection": "force",
-    "jsx": "react-jsx",
-    "allowJs": true,
-    "types": ["bun"],
-
-    // Bundler mode
-    "moduleResolution": "bundler",
-    "allowImportingTsExtensions": true,
-    "verbatimModuleSyntax": true,
-    "noEmit": true,
-
-    // Best practices
-    "strict": true,
-    "skipLibCheck": true,
-    "noFallthroughCasesInSwitch": true,
-    "noUncheckedIndexedAccess": true,
-    "noImplicitOverride": true,
-
-    // Some stricter flags (disabled by default)
-    "noUnusedLocals": false,
-    "noUnusedParameters": false,
-    "noPropertyAccessFromIndexSignature": false
-  }
+  "files": [],
+  "references": [
+    { "path": "./tsconfig.app.json" },
+    { "path": "./tsconfig.node.json" }
+  ]
 }