feat(scholars): add multiselect and bulk actions (delete, toggle, export)

Add Set<number>-based selection state to ScholarsPage with checkboxes
in both table and card views, select-all toggle, and stale-key pruning.

Backend: POST /scholars/bulk-delete, POST /scholars/bulk-toggle, and
GET /scholars/export?ids= filter. Service functions use user-scoped
queries. Structured logging for bulk operations.

Frontend: useScholarBulkActions composable extracts selection and bulk
action logic. AppSelect-based action dropdown with dynamic options.
Delete prompts window.confirm; enable/disable applies immediately.
Export downloads filtered JSON.

Includes integration tests for all bulk endpoints and frontend unit
tests for selection toggle, select-all, and stale pruning.

app/api/schemas/scholars.py

@@ -126,6 +126,33 @@ class DataExportEnvelope(BaseModel):
     model_config = ConfigDict(extra="forbid")
 
 
+class ScholarBulkIdsRequest(BaseModel):
+    scholar_profile_ids: list[int] = Field(..., min_length=1, max_length=500)
+
+    model_config = ConfigDict(extra="forbid")
+
+
+class ScholarBulkToggleRequest(BaseModel):
+    scholar_profile_ids: list[int] = Field(..., min_length=1, max_length=500)
+    is_enabled: bool
+
+    model_config = ConfigDict(extra="forbid")
+
+
+class ScholarBulkCountData(BaseModel):
+    deleted_count: int = 0
+    updated_count: int = 0
+
+    model_config = ConfigDict(extra="forbid")
+
+
+class ScholarBulkCountEnvelope(BaseModel):
+    data: ScholarBulkCountData
+    meta: ApiMeta
+
+    model_config = ConfigDict(extra="forbid")
+
+
 class DataImportRequest(BaseModel):
     schema_version: int | None = None
     exported_at: str | None = None