[namedgraph]

Adds DELETE(url: URI) → Result, following the conventions of POST/PUT/PATCH.

• Spec (formal-semantics.md): a §4.4 entry; DELETE added to the update effects (§3.6), the write row of the error table (§3.7) and the upper-case HTTP method names (§4). §5 notes that REST-VKG does not implement it yet.
• Behaviour: as the Graph Store Protocol's DELETE. It goes through the client's conditional write path (HEAD → If-Match). It returns the one-row status/url result, with url being the URI removed. Any non-2xx answer is a ValueError, 404 for a missing document included; there is no if_absent. It counts as a write to its URI for the ForEach same-target rule. Kind: destructive.
• Guide: a ## DELETE(url: URI) → Result section with an example, which the guide tests run.
• Tests: DELETE joins the shared write contract (test_write_contract.py). New tests/unit/test_delete.py covers the type errors, the 404, the JSON arguments and the ForEach cases. The name and kind tests include it. tests/test_client_writes.py is removed: it existed because no operation sent a DELETE, and the write contract now covers its If-Match check.
• CHANGELOG.md: a new 2.0.4 - Unreleased section. README.md: DELETE added to the operation list.

ruff check and the offline suite pass (1154 passed, 7 skipped). Not run yet:

• -m ldh against a LinkedDataHub, to see its answer to DELETE (e.g. on a container with children).
• The REST-VKG counterpart.

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