test(schemas): check schemas against Draft-07

[LKSNDRTMLKV]

Closes #379.

Every product group schema declares Draft-07, but schema_conformity.rs only showed that each one compiles in the library that enforces it. That is circular: a schema the library tolerates and Draft-07 forbids would have passed. This adds the two independent checks the issue asked for, and makes the register's first conformance claim under the rule from #378.

What runs

crates/dpp-tests/tests/json_schema_draft07.rs, in just check:

Test	Holds
every_shipped_schema_declares_draft07_and_is_compiled_as_draft07	every schema declares Draft-07, and the registry's validator_for resolves each to Draft-07
every_shipped_schema_is_valid_against_the_draft07_metaschema	each validates against the official meta-schema
the_metaschema_check_rejects_what_it_is_for	the check rejects a bad type, required, minimum, minLength, enum, pattern and additionalProperties, at any depth
the_metaschema_ignores_a_misspelt_keyword	asserts the meta-schema's blind spot: Draft-07 permits unknown keywords
every_keyword_and_format_a_schema_uses_has_its_suite_file_vendored	closes that blind spot: fails on any keyword that is not Draft-07's, and on any used keyword or format whose suite file is not vendored, naming the file
every_vendored_suite_case_passes	22 official suite files, 153 groups and 710 cases, against the pinned jsonschema crate. All pass and none is excluded
the_suite_harness_reports_what_it_is_for	the harness reports a wrong verdict and a schema that does not compile
every_ref_in_a_shipped_schema_is_local	the workspace builds jsonschema without remote retrieval, so no schema may leave its document
the_vendored_files_are_the_bytes_recorded_here	sizes and SHA-256 match NOTICE.md, and an unrecorded file fails

Everything passed on the first run, so no schema changed. I also broke it on purpose and reverted: a flipped suite verdict, a removed suite file, and a misspelt keyword plus an invalid type planted in a shipped schema were each caught, with a message naming the problem.

Vendored files

crates/dpp-tests/fixtures/json-schema/ holds:

• the Draft-07 meta-schema from json-schema.org;
• the files of json-schema-org/JSON-Schema-Test-Suite (MIT) at commit 5b0ee1613e45fcc2bddac00e07c19cd49b00d8a8 for the keywords and formats the schemas use, with its LICENSE.

That is 164 KB in all. Source, retrieval date, size and SHA-256 of each file are in NOTICE.md, and .gitattributes pins them -text, as it does for the vendored AAS schemas. Only the files in use are vendored. When a schema needs another, the census above fails and names the file to take. crates/dpp-tests is not published.

The register

The JSON Schema row of docs/architecture/STANDARDS.md now reads Yes, with its class, scope and known deviations, and the statement that it is self-declared. It is the first claim in the register. Not run: the keywords no schema uses (patternProperties, if/then/else and others), and remote $ref retrieval.

Two edits outside the new test

• standard_citations.rs skips the vendored suite directory. The suite's own text mentions RFC 8141 in its URN cases, which the tripwire counted as this repository citing it, and a register row would claim the code implements URN syntax. The files' bytes are held by their hashes instead. The skip and its reason are in the module docs.
• sha2 and hex, both already in the workspace, are added as dev-dependencies of dpp-tests for the hash check.

just check is green: 1716 tests, plus the plugin suites.