WP-00: project skeleton with three-level test harness

Cargo workspace (domain, application, infrastructure, api), axum health endpoint
with SPA fallback, Vue 3 + Tailwind frontend, Vitest, Playwright, Makefile,
Gitea Actions CI and README.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/Cargo.toml

@@ -0,0 +1,39 @@
+[workspace]
+resolver = "2"
+members = ["crates/domain", "crates/application", "crates/infrastructure", "crates/api"]
+
+[workspace.package]
+version = "0.1.0"
+edition = "2021"
+license = "Proprietary"
+
+[workspace.dependencies]
+domain = { path = "crates/domain" }
+application = { path = "crates/application" }
+infrastructure = { path = "crates/infrastructure" }
+
+anyhow = "1"
+async-trait = "0.1"
+axum = { version = "0.8", features = ["macros"] }
+base64 = "0.22"
+chrono = { version = "0.4", features = ["serde"] }
+dotenvy = "0.15"
+http-body-util = "0.1"
+jsonwebtoken = "9"
+argon2 = "0.5"
+rand = "0.8"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+sha2 = "0.10"
+sqlx = { version = "0.8", features = ["runtime-tokio", "sqlite", "chrono", "uuid", "migrate"] }
+thiserror = "2"
+tokio = { version = "1", features = ["full"] }
+tower = { version = "0.5", features = ["util"] }
+tower-http = { version = "0.6", features = ["fs", "trace", "cors"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+utoipa = { version = "5", features = ["axum_extras", "uuid", "chrono"] }
+uuid = { version = "1", features = ["v4", "serde"] }
+
+[workspace.lints.clippy]
+all = "warn"