chore: clean up repo organization

- Standardize on bun: remove package-lock.json, add packageManager field,
  gitignore non-bun lockfiles, fix stray npm install in android:build:clean
- Remove stale build logs and empty dirs (src-tauri/plugins, docs/tickets)
- Move android-dev.sh into scripts/
- Consolidate root docs into docs/ (docker/builder under docs/build/);
  move the architecture overview to docs/architecture/README.md
- Extract Requirements Specification from README into docs/requirements.md
  and slim README down to a project intro + docs index
- Fix internal references to the moved files

package.json

@@ -3,6 +3,7 @@
   "version": "0.1.0",
   "description": "",
   "type": "module",
+  "packageManager": "bun@1.3.5",
   "scripts": {
     "dev": "vite dev",
     "build": "vite build",
@@ -18,7 +19,7 @@
     "test:rust": "./scripts/test-rust.sh",
     "android:build": "./scripts/build-android.sh",
     "android:build:release": "./scripts/build-android.sh release",
-    "android:build:clean": "rm -rf node_modules/.vite dist .svelte-kit .next build target src-tauri/target && npm install && npm run build",
+    "android:build:clean": "rm -rf node_modules/.vite dist .svelte-kit .next build target src-tauri/target && bun install && bun run build",
     "android:deploy": "./scripts/deploy-android.sh",
     "android:dev": "./scripts/build-and-deploy.sh",
     "android:check": "./scripts/check-android.sh",