chore: initial project scaffold

Set up Mangalord with a Rust/axum backend, SvelteKit frontend, Postgres,
and Docker Compose deployment. Establishes the architecture and TDD
patterns the project will extend:

- Hexagonal-ish backend layering (domain / repo / storage / api) with
  a pluggable Storage trait (LocalStorage today, S3 as a future impl).
- Initial migration: users, mangas, chapters, bookmarks.
- Vertical slice for mangas (list, search, create, get) with
  #[sqlx::test] integration coverage and storage unit tests.
- SvelteKit frontend using Svelte 5 runes, typed API client, Vitest
  unit tests and Playwright e2e with route mocking.
- CLAUDE.md documenting layering, TDD/git/SemVer workflow rules, and
  extension points (tags, fulltext search, OCR, S3, auth).
- Project-scoped .claude/settings.json with permission allowlist for
  the toolchain (git, cargo, npm/vite, docker, psql, gh, doc fetches).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.env.example

@@ -0,0 +1,15 @@
+# Copy to .env for `docker compose up`.
+# Local dev (cargo run / npm run dev) reads backend/.env if present.
+
+POSTGRES_USER=mangalord
+POSTGRES_PASSWORD=mangalord
+POSTGRES_DB=mangalord
+
+DATABASE_URL=postgres://mangalord:mangalord@postgres:5432/mangalord
+BIND_ADDRESS=0.0.0.0:8080
+STORAGE_DIR=/var/lib/mangalord/storage
+RUST_LOG=info,mangalord=debug
+
+# Public base URL the frontend uses to reach the API from the browser.
+# In docker compose this is exposed on the host.
+PUBLIC_API_BASE=http://localhost:8080/api