feat(app): unify desktop shell with webapp

[lostmygithubaccount]

Summary

• replace the iced desktop GUI with a Tauri 2 shell around the local bookmarks webapp
• expose reusable webapp router/server entrypoints and add /api/health
• keep TOML storage/Python/CLI compatibility while bumping the release to 0.5.0
• update CI/release scripts for Tauri prerequisites and core -> webapp -> app -> cli publish order

Verification

• cargo fmt --all -- --check
• cargo test --workspace --features app,webapp
• cargo clippy --workspace --all-targets --features app,webapp -- -D warnings
• cargo check --features app,webapp --locked
• uv run maturin develop
• uv run --only-group dev ruff check .
• uv run --only-group dev ruff format --check .
• uv run ty check
• uv run pytest
• cargo package -p dkdc-bookmarks-core --allow-dirty
• cargo publish -p dkdc-bookmarks-core --dry-run --allow-dirty