feat(v3): migrate workspace to API, Tauri desktop, and v3 crates; remove legacy MCP stack

- Add apps/api, desktop Tauri shell, domain/application/crypto/device-auth/infrastructure-db
- Replace desktop-daemon vault integration; drop secrets-core and secrets-mcp*
- Ignore apps/desktop/dist and generated Tauri icons; document icon/dist steps in AGENTS.md
- Apply rustfmt; fix clippy (collapsible_if, HTTP method as str)

apps/api/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "secrets-api"
+version = "0.1.0"
+edition.workspace = true
+
+[[bin]]
+name = "secrets-api"
+path = "src/main.rs"
+
+[dependencies]
+anyhow.workspace = true
+axum.workspace = true
+dotenvy.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+sqlx.workspace = true
+tokio.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+uuid.workspace = true
+chrono.workspace = true
+reqwest.workspace = true
+
+secrets-application = { path = "../../crates/application" }
+secrets-device-auth = { path = "../../crates/device-auth" }
+secrets-domain = { path = "../../crates/domain" }
+secrets-infrastructure-db = { path = "../../crates/infrastructure-db" }