Release v0.5.0

[roelvangils]

Summary

First tagged release. Feature-complete for the v1 candidate.

After this PR merges, push the `v0.5.0` tag (`git tag v0.5.0 && git push origin v0.5.0`) and the release workflow builds unsigned binaries for Linux x86_64, macOS arm64 (with Metal Whisper acceleration), and Windows x86_64, attaching each to a GitHub Release of the same name.

Changes in this PR

• Workspace `version` bumped from `0.1.0-dev` to `0.5.0`. All internal path-deps in `crates/*/Cargo.toml` updated to match.
• `CHANGELOG.md` `[Unreleased]` section renamed to `[0.5.0] - 2026-05-06`. A fresh empty `[Unreleased]` block stays on top for ongoing work.

What ships in 0.5.0

End-to-end DAISY 2.02 → EPUB 3 conversion with Media Overlays, plus:

• Validators bundled. `dpub validate` (EPUBCheck) and `dpub a11y` (ACE) with stable `--json` output. Output is EPUBCheck-clean (0/0/0) on the reference 11h45m audiobook where Pipeline 2 emits 2 errors + 31 warnings on the same input.
• Audio. Optional MP3 → Opus re-encoding with parallel ffmpeg (`--audio opus --bitrate `); `-map_metadata 0` preserves source ID3 tags across the format change.
• Transcription. Local Whisper via whisper.cpp (`--transcribe --whisper-model `) with prose-shaped paragraph cleanup by default (`--no-text-cleanup` for raw debug output). One model load per book, not per file.
• Cover. `--cover ` for an explicit local image; `--auto-cover` for best-effort lookup via Open Library.
• Rights. `--rights ""` stamps a free-text `dc:rights` element.
• Catalogue. `dpub batch -o ` walks a directory and converts every DAISY book in parallel via rayon, with per-book error recovery and a JSON summary.
• Apple Silicon GPU. `cargo build --release --features metal` for ~5–10× faster transcription on M-series.

No API stability commitment yet — that comes with 1.0.

Out of scope

• Code signing on macOS. Binaries from this release will be unsigned; users authorise once on first run via System Settings → Privacy & Security, or build from source.
• Cargo.io publishing. Most workspace crates are internal and only `dpub-cli` would make sense to publish; deferred decision.

Test plan

• `cargo build --workspace` clean.
• `cargo test --workspace` clean.
• `cargo clippy --all-targets -- -D warnings` clean.
• After merge: tag push fires the release workflow; verify each platform's artefact runs (`dpub --version` prints `dpub 0.5.0`, `dpub info ` works).