feat(docs): nested-entity 'This deal' / 'From client' split (B4 #8 phase 4)

Finishes B4 #8 by completing the UI half of the per-interest filing
model. Backend foundations (files.interest_id column, ensureEntityFolder
for 'interest', upload-zone scope radio, outcome rename hook, backfill)
shipped earlier in this audit cycle.

- listFiles validator + service: optional interestId filter
- listFilesAggregatedByEntity: routes entityType='interest' to a new
  helper that returns "THIS DEAL" + "FROM CLIENT" + symmetric-reach
  company/yacht groups
- InterestDocumentsTab: Attachments section now renders two cohorts
  via two paginated queries, with client-side de-duplication so files
  filed under this deal don't double-count under "From client"
- FileRow type exposes the optional interestId so the de-dupe filter
  doesn't need a re-fetch

src/lib/validators/files.ts

@@ -23,14 +23,18 @@ export const listFilesSchema = baseListQuerySchema
     clientId: z.string().optional(),
     yachtId: z.string().optional(),
     companyId: z.string().optional(),
+    interestId: z.string().optional(),
     category: z.string().optional(),
     folderId: z
       .string()
       .uuid()
       .optional()
       .transform((v) => (v === '' ? null : v)),
-    /** Entity-aggregated projection params - mutually exclusive with folderId. */
-    entityType: z.enum(['client', 'company', 'yacht']).optional(),
+    /** Entity-aggregated projection params - mutually exclusive with folderId.
+     *  'interest' splits direct-attached into "This deal" (files.interestId
+     *  matches) and "From client" (client-level + other deals); the other
+     *  values fall through to the legacy symmetric-reach aggregator. */
+    entityType: z.enum(['client', 'company', 'yacht', 'interest']).optional(),
     entityId: z.string().uuid().optional(),
   })
   .refine(