refactor: DDD/CQRS architecture, unified crate layout

- crates: common→application, api→presentation, infrastructure/*→adapters/*
- new crates: api-types, infra-wiring
- domain: errors/, models/, value_objects/, ports/, services/
- application: CQRS use cases (songs/, tabs/) w/ commands, queries, deps
- unified DomainError replaces RepositoryError
- workspace deps, unused dep cleanup
- fix: parse plain-text chord lines (UG drops spans mid-song)
- tests extracted to separate modules (tests/ dirs)

crates/infra-wiring/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "infra-wiring"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

crates/infra-wiring/src/config.rs

@@ -0,0 +1,54 @@
+use std::env;
+
+#[derive(Debug)]
+pub struct AppConfig {
+    pub database_url: String,
+    pub host: String,
+    pub port: u16,
+    pub cors_origins: CorsOrigins,
+}
+
+#[derive(Debug)]
+pub enum CorsOrigins {
+    Any,
+    List(Vec<String>),
+}
+
+impl AppConfig {
+    pub fn from_env() -> Self {
+        let database_url =
+            env::var("DATABASE_URL").unwrap_or_else(|_| "sqlite://./pocket-chords.db".into());
+
+        let host = env::var("HOST").unwrap_or_else(|_| "0.0.0.0".into());
+
+        let port = env::var("PORT")
+            .ok()
+            .and_then(|v| v.parse::<u16>().ok())
+            .unwrap_or(8000);
+
+        let cors_origins = match env::var("CORS_ALLOWED_ORIGINS")
+            .unwrap_or_else(|_| "*".into())
+            .trim()
+            .to_string()
+        {
+            s if s == "*" => CorsOrigins::Any,
+            s => CorsOrigins::List(
+                s.split(',')
+                    .map(|o| o.trim().to_string())
+                    .filter(|o| !o.is_empty())
+                    .collect(),
+            ),
+        };
+
+        Self {
+            database_url,
+            host,
+            port,
+            cors_origins,
+        }
+    }
+
+    pub fn bind_addr(&self) -> String {
+        format!("{}:{}", self.host, self.port)
+    }
+}

crates/infra-wiring/src/lib.rs

@@ -0,0 +1,3 @@
+pub mod config;
+
+pub use config::{AppConfig, CorsOrigins};