[Subtask] Add Semantic Model list, alter, and drop operations in Gravitino Core

### Describe the subtask

Add managed Core operations for listing, altering, and dropping Semantic Models. Alter applies ordered changes atomically, preserves audit metadata, and performs complete write validation only when replacing the definition. Metadata-only changes do not resolve external sources.

This subtask includes dispatcher integration and focused unit and JDBC tests. Create, load, REST APIs, and clients are out of scope.

### Parent issue

#12209

Start by locating existing Core list, alter, and drop operations for neighboring model types, then trace their dispatcher integration. Review the focused unit and JDBC test patterns before implementing the Semantic Model scope. Done means ordered alters are atomic, audit metadata is preserved, validation is limited as specified, and the focused tests pass.

Written by the indexing model from the issue text.