feat: unify artifact family reads and registration

[Zxf-xufeng]

Which issue or RFC does this PR close?\n\nImplements RFC #1549.\n\n## Rationale for this change\n\nTopic Memory is already stored as an Artifact but was not accepted by the standard artifact read contract. Built-in Artifact family registration was also hard-coded in runtime composition, making future family additions easy to miss.\n\n## What changes are included in this PR?\n\n- Adds topic-memory to the shared read-only Artifact family contract for list, get, revision list, and revision get.\n- Adapts the existing published Topic Memory browse projection to list_artifacts, including title, summary, publication time, source count, and signed cursor pagination.\n- Keeps Topic Memory standard writes disabled and preserves the specialized search/get/flush APIs.\n- Adds ArtifactFamilyDefinition and ArtifactFamilyRegistry; runtime ArtifactRepository composition now consumes the built-in registry.\n- Keeps Source registration on the existing SourceDefinitionRegistry.\n- Regenerates checked-in API models/schema and adds contract, registry, persistence, and server regression coverage.\n\n## Are there any user-facing changes?\n\nYes. GET /v1/scopes/{scope_id}/artifacts/topic-memory and the corresponding standard read/revision routes now accept Topic Memory. Topic Memory list items expose optional display metadata. Existing family behavior and specialized Topic Memory endpoints remain compatible.\n\n## How was this change tested?\n\n- make contract-test\n- uv run ty check\n- uv run ruff check ... and uv run ruff format --check ...\n- Targeted persistence and contract tests: 105 passed\n- env -u POWERCONTEXT_SERVER_DASHBOARD_ENABLED -u POWERCONTEXT_SERVER_AUTH_ENABLED -u POWERCONTEXT_SERVER_AUTH_TOKEN -u POWERCONTEXT_CLIENT_API_TOKEN -u POWERCONTEXT_CODEX_AUTHORIZATION uv run pytest tests/test_topic_memory_server.py -q (7 passed)\n- env -u POWERCONTEXT_SERVER_DASHBOARD_ENABLED -u POWERCONTEXT_SERVER_AUTH_ENABLED -u POWERCONTEXT_SERVER_AUTH_TOKEN -u POWERCONTEXT_CLIENT_API_TOKEN -u POWERCONTEXT_CODEX_AUTHORIZATION uv run pytest tests/test_access_http.py -q (18 passed)\n- Full make test was attempted; 1892 passed, 61 skipped, and 175 environment/platform failures occurred because the session injected Dashboard/Auth settings and systemd tests run on macOS.\n\n## AI usage statement\n\nCreated with OpenAI Codex assistance; the implementation and final scope are reviewed by the repository owner.