fix(import): company-scope the bank_file_imports dedup key (#925)

* fix(import): company-scope the bank_file_imports dedup key

The bank_file_imports unique constraint was (user_id, file_hash), predating
multi-tenancy: a user importing the same statement file into a second company
hit an upsert that resolved onto the first company's row, which RLS rejected
(42501). Widen it to (company_id, file_hash) - the swap 20260330130000 made for
sie_imports but missed here - and drop the now-obsolete
BANK_IMPORT_DUPLICATE_OTHER_COMPANY cross-company pre-check from the v1 route
(the structured-error code stays for API compat).

The migration was already applied to prod; committing it reconciles the orphan
(prod schema_migrations had 20260707130000 with no matching repo file).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* docs(import): fix stale unique-constraint comment (CodeRabbit)

The completion-update comment still described the old (user_id, file_hash)
constraint; it is (company_id, file_hash) since 20260707130000.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/api/import/bank-file/execute/route.ts

@@ -79,7 +79,7 @@ export const POST = withRouteContext(
           status: 'processing',
           date_from: transactions.map((t) => t.date).sort()[0] || null,
           date_to: transactions.map((t) => t.date).sort().reverse()[0] || null,
-        }, { onConflict: 'user_id,file_hash' })
+        }, { onConflict: 'company_id,file_hash' })
         .select()
         .single()