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)

Dockerfile

@@ -1,10 +1,10 @@
-FROM rust:1.92 AS builder
+FROM rust:1.97 AS builder
 
 WORKDIR /app
 COPY . .
 
 # Build the release binary
-RUN cargo build --release -p api
+RUN cargo build --release -p presentation
 
 FROM debian:trixie-slim
 
@@ -17,7 +17,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     libsqlite3-0 \
     && rm -rf /var/lib/apt/lists/*
 
-COPY --from=builder /app/target/release/api .
+COPY --from=builder /app/target/release/presentation .
 
 
 # Create data directory for SQLite
@@ -27,4 +27,4 @@ ENV DATABASE_URL=sqlite:///app/data/pocket-chords.db
 
 EXPOSE 8000
 
-CMD ["./api"]
+CMD ["./presentation"]