fix: prevent snowflake→snowflake vendor_bridge false positive; improve Databricks limitations

Add read-side none override for snowflake on vendor_bridge to prevent
combine(full, full) = full for the snowflake→snowflake pair.
Sharpen DBR version string and add manual refresh limitation.

Author: b-per

src/data/compatibility.test.ts

@@ -213,4 +213,8 @@ describe('vendor_bridge catalog', () => {
     expect(entry?.sourceUrl).toBeDefined();
     expect(entry?.sourceUrl?.length).toBeGreaterThan(0);
   });
+
+  it('snowflake cannot read vendor_bridge (not a Catalog Federation consumer)', () => {
+    expect(engineReadRules.snowflake?.vendor_bridge?.support).toBe('none');
+  });
 });

src/data/compatibility.ts

@@ -144,6 +144,9 @@ export const engineCatalogRules: Record<EngineId, EngineRule> = {
 // Read-side overrides: where an engine's READ catalog capability differs from its WRITE capability.
 // Most engines: same rules both ways. Exceptions captured here.
 export const engineReadRules: Partial<Record<EngineId, Partial<EngineRule>>> = {
+  snowflake: {
+    vendor_bridge: { support: 'none', limitations: [] },
+  },
   databricks: {
     // Databricks can READ from external REST catalogs (including BigLake Metastore) via Spark,
     // even though it cannot WRITE to them.
@@ -164,10 +167,11 @@ export const engineReadRules: Partial<Record<EngineId, Partial<EngineRule>>> = {
     ]},
     vendor_bridge: { support: 'partial', limitations: [
       'Requires Snowflake Catalog Federation configured in Unity Catalog (foreign catalog)',
-      'Databricks Runtime 13.3 LTS+ or Databricks SQL 2023.40+ required',
+      'Databricks Runtime 13.3 LTS+ or Databricks SQL 2023.40+ required; DBR 16.4 LTS+ recommended for full feature support',
       'External location in Unity Catalog must cover the Snowflake table storage path',
       'Non-Iceberg Snowflake tables permanently fall back to JDBC query federation (slower)',
       'Tables with URI-incompatible locations or unsupported storage schemes also fall back to JDBC',
+      'Foreign Iceberg tables require manual metadata refresh (ALTER TABLE) to reflect Snowflake writes in Databricks',
     ], sourceUrl: 'https://docs.databricks.com/aws/en/query-federation/snowflake-catalog-federation' },
   },
 };