test: add CI guard for manifest.name parity and global uniqueness (#280)

[UroojFatima-052]

Closes #280

Adds a static YAML scan under tests/test_registry_identity.py that runs as part of pytest tests/ in CI. Two independent tests, following the discovery pattern from tests/test_skill_issuer.py.

Changes

tests/test_registry_identity.py (new)

• test_registry_manifest_name_matches_path, for every registry-layout skill (skills/<category>/<skill_name>/), asserts manifest.name equals the path-derived registry ID. Whitespace-only names are treated as missing (strip first). Flat layouts are skipped since _expected_registry_id returns None for them.
• test_registry_manifest_names_are_globally_unique, groups skill paths by manifest.name using defaultdict(list); asserts no name has more than one path. Duplicate failures report both conflicting paths.
• Failure messages use paths relative to REPO_ROOT for readability in CI logs.
• Both tests batch their errors (collect all violations, then assert once) so a single CI run surfaces every bad skill instead of failing on the first one.

docs/TESTING.md

• Added test_registry_identity.py row to the Status table.
• Added a one-line description under the Framework test section.

CHANGELOG.md

• Added entry under [Unreleased] > Added.

Notes

• No loader behavior changes, kept warn-only per v1 scope.
• Both tests pass locally on current main (2 passed in 0.47s).
• black --check and flake8 clean.
• Did not touch out-of-scope items: load_skill_by_id(), index.json, or promoting SkillwareIdentityWarning to a hard error.