chore: migrate to v3, Doppler secrets, clean up legacy code

- Remove all pre-v3 code: scraper, ui-v2, backend v1, ios v1+v2, legacy CI workflows
- Flatten v3/ contents to repo root
- Add Doppler secrets management (project=libnovel, config=prd)
- Add justfile with doppler run wrappers for all docker compose commands
- Strip hardcoded env fallbacks from docker-compose.yml
- Add minimal README.md
- Clean up .gitignore

ui/components.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://shadcn-svelte.com/schema.json",
+  "style": "default",
+  "tailwind": {
+    "config": "",
+    "css": "src/app.css",
+    "baseColor": "zinc",
+    "cssVariables": false
+  },
+  "aliases": {
+    "components": "$lib/components",
+    "utils": "$lib/utils",
+    "ui": "$lib/components/ui",
+    "hooks": "$lib/hooks"
+  },
+  "typescript": true
+}