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)

crates/device-auth/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "secrets-device-auth"
+version = "0.1.0"
+edition.workspace = true
+
+[lib]
+name = "secrets_device_auth"
+path = "src/lib.rs"
+
+[dependencies]
+anyhow.workspace = true
+hex.workspace = true
+rand.workspace = true
+sha2.workspace = true
+url.workspace = true
+uuid.workspace = true