[SYNPY-1869] Add SearchIndex entity + search-management APIs; rename SchemaOrganization to Organization

[BryanFauble]

Problem:

Two related gaps in the OOP model layer:

1. SearchIndex / search-management surface was incomplete. The SearchManagementController in Synapse-Repository-Services exposes a family of resources — SearchIndex (an OpenSearch index built from a defining SQL query), plus the configuration resources that control how indexes are built: TextAnalyzer, ColumnAnalyzerOverride, SynonymSet, SearchConfiguration, and SearchConfigBinding — as well as index query and autocomplete endpoints. The Python client only had a partial, not-fully-correct starting point for these.

2. SchemaOrganization naming was inconsistent. The model that holds JSON-schema resources was named SchemaOrganization, but conceptually it's just an "Organization" that holds resources. The name should read consistently.

Solution:

Search management (new):

• Added the SearchIndex entity model (models/search_index.py) following the async-first @async_to_sync pattern — store/get/delete/autocomplete, columns derived read-only from defining_sql, registered concrete type org.sagebionetworks.repo.model.search.table.SearchIndex.
• Added the search-management resource models (models/search_management.py): TextAnalyzer, ColumnAnalyzerOverride, SynonymSet, SearchConfiguration, SearchConfigBinding, plus query/autocomplete request+hit types.
• Added the REST API layer (api/search_services.py) and wired it into api/__init__.py.
• Registered the new entity in concrete_types.py, entity_factory.py, mixins/asynchronous_job.py, and marked SearchIndex read-only-schema in mixins/table_components.py.

Rename (hard, no back-compat alias):

• SchemaOrganization → Organization (class + SchemaOrganizationProtocol → OrganizationProtocol), module helper list_json_schema_organizations → list_organizations.
• Renamed files via git mv to preserve history: models/schema_organization.py → models/organization.py, the unit/integration test modules, and docs/reference/experimental/{async,sync}/schema_organization.md → organization.md; updated mkdocs.yml nav.
• Updated all references across models/__init__.py, operations/{store,delete}_operations.py, mixins, curator extension, and the deprecated services/json_schema.py docstring pointers.
• Note: the legacy public JsonSchemaOrganization class in services/json_schema.py is intentionally left unchanged — it is a separate deprecated API, not the model being renamed.

Testing:

• New async unit tests for the search-management models and Organization; existing store/delete/factory routing unit tests updated for the rename.
• Focused unit run green: 142 passed across json_schema services, organization, search-management, and store/delete operations.
• Integration tests added for SearchIndex (create/retrieve, match-all query, autocomplete, delete) — kept minimal to limit CI/Synapse-server load; index-creation tests skip gracefully on a 403 where creation is restricted.
• ruff and black clean on all changed files (the 2 remaining F841 flags in the renamed org test module and the json_schema tutorial are pre-existing debt, left untouched per surgical-change scope).