feat: finalize identity-free graph model

[savasp-agent]

Summary

• expose the exact selection-based mutation and endpoint-intent relationship creation surface
• remove universal entity IDs, relationship endpoint/direction state, ID-targeted CRUD, and merge-by-ID behavior
• migrate repository fixtures and examples to keyless or explicit domain selectors across all in-tree providers
• persist native logical labels/types while keeping provider identity private and marker-owned complex storage isolated

Validation

• Fast lane: 2,383 tests
• Neo4j provider suite: 585 tests
• AGE provider suite: 687 tests (678 passed, 9 capability skips)
• PackageValidation.proj Validate target
• Pre-push Release build and dotnet format --verify-no-changes

Follow-up

#482 owns the consolidated documentation and alpha recreate/reimport migration boundary after #481 and #498. This PR limits documentation changes to XML docs and compiled examples.

Closes #477, closes #478, closes #479, closes #480.

[savasp-agent]

Review takeover closure

Final reviewed head: 5fbf86d3033a38571e9184142f6a15e14b19160e

I reviewed the complete PR diff and its linked acceptance scope (#477–#480), audited the public surface, serialization/codegen, all three providers, examples, release/package paths, transaction ownership, atomicity/locking order, and repository-wide legacy-identity remnants. There were no pre-existing review threads or submitted reviews to resolve.

ID	Severity	Origin	Final disposition	Implementation evidence
F-001	Blocking	Takeover review	Fixed	Migrated the release-only examples/SimpleMovieExample from removed entity IDs/endpoint constructors and one-argument relationship creation to endpoint-free relationships plus exact-one selector-based CreateRelationshipAsync calls.
F-002	Nit	Takeover review	Fixed	Removed the now-unused in-memory logger field, initialization, and NullLogger import left behind by the deleted legacy CRUD paths.

Verification on the final patch:

• SimpleMovieExample Debug build: passed.
• Focused Graph.InMemory.Tests: 516 total, 515 passed, 1 declared capability skip.
• Full serial all-provider lane: 3,655 total, 3,643 passed, 12 declared capability skips; Neo4j and AGE both passed.
• Package validation: exact 9-package inventory, package/assembly metadata, and clean package-reference solution build passed.
• Clean Release consumer restore/build against the locally produced PR packages: passed.
• Pre-push Release warnings-as-errors build and format verification: passed.
• Refreshed hosted checks: all passed, including build/test, three-platform package validation, docs, dependency review, repository automation, and CodeQL.

Final ledger: 2 fixed, 0 deferred, 0 rejected, 0 unresolved. The already-declared documentation/migration-boundary work remains tracked in #482 and was not expanded into this PR.

Verdict: the reviewed implementation meets its declared scope and is ready for the required external approval.