feat(books): add primary file size filter rule

Add fileSize as a filterable rule field resolved against the book's primary file size in bytes. In the filter builder UI, allow operators to input sizes in megabytes with automatic serialization to bytes for queries.

server/test/book-api-contract.e2e-spec.ts

@@ -1,7 +1,7 @@
 import { randomUUID } from 'crypto';
 
 import { eq } from 'drizzle-orm';
-import { rm } from 'fs/promises';
+import { rm, stat } from 'fs/promises';
 import { join } from 'path';
 
 import * as unzipper from 'unzipper';
@@ -317,6 +317,33 @@ describe('Book API contract (e2e)', { timeout: SCENARIO_TIMEOUT_MS }, () => {
 
       expectError(invalidLimit, 400, 'limit must not be greater than 20');
     });
+
+    it('filters books by the selected primary file size', async () => {
+      const primaryFileSize = (await stat(visibleEpub.absolutePath)).size;
+      const response = await ctx.app.inject({
+        method: 'POST',
+        url: '/api/v1/books/query',
+        headers: authHeader(limitedUser.accessToken),
+        payload: {
+          filter: {
+            type: 'group',
+            join: 'AND',
+            rules: [
+              { type: 'rule', field: 'title', operator: 'eq', value: 'Alpha Contract EPUB' },
+              { type: 'rule', field: 'fileSize', operator: 'eq', value: primaryFileSize },
+            ],
+          },
+          sort: [{ field: 'title', dir: 'asc' }],
+          pagination: { page: 0, size: 10 },
+        },
+      });
+
+      expect(response.statusCode).toBe(201);
+      expect(response.json()).toMatchObject({
+        total: 1,
+        items: [{ id: visibleEpub.bookId, files: [{ id: visibleEpub.bookFileId, role: 'primary', sizeBytes: primaryFileSize }] }],
+      });
+    });
   });
 
   describe('bulk query selections', () => {