Fix P0 issues in financial ingestion architecture

- Wrap snapshot updates in transactions with error context for each child table
- Add sidecar retry with exponential backoff (3 attempts, 2s base, 10s max, 30% jitter)
- Add HTTP timeout (30s per request) and SEC rate limiting (10 req/s) in Rust
- Add XBRL validation with status reporting (checks root element, tag balance)

lib/server/taxonomy/engine.test.ts

@@ -49,6 +49,9 @@ function createHydrationResult(): TaxonomyHydrationResult {
       unmapped_row_count: 0,
       material_unmapped_row_count: 0,
       warnings: ['rust_warning']
+    },
+    xbrl_validation: {
+      status: 'passed'
     }
   };
 }