Refactor wiki schema and search migrations

[humandebri]

Purpose

Refactor the wiki storage terminology, schema migrations, and search/index synchronization on top of the canonical wiki flow branch.

Changes

• Rename and align memory/store-facing docs and APIs around the Store terminology.
• Update VFS schema, runtime migration, and sync/search paths.
• Refresh generated Candid/IDL client surfaces and related browser/extension clients.
• Add tests for migration, sync, store, and runtime behavior touched by the refactor.

Validation

• Not run in this PR creation step.

Impact

• Base branch: improve/wiki-review-canonical-flow.
• Scope affects VFS runtime/store schema handling, generated API surfaces, docs, and clients.