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/crates/application/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "application"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+domain.workspace = true
+async-trait.workspace = true
+base64.workspace = true
+chrono.workspace = true
+rand.workspace = true
+sha2.workspace = true
+uuid.workspace = true
+
+[dev-dependencies]
+tokio.workspace = true
+
+[lints]
+workspace = true

backend/crates/application/src/lib.rs

@@ -0,0 +1 @@
+//! application layer