feat(ui): Data Sources UI — enterprise browser for all 5 source databases

New "Data Sources UI" tab with per-database Browser (catalog + sample data),
Query Console (SqlWorkbench) and embedded interactive Shell (DbShell via SSH).

Backend:
- Extend sql_console.py with Cassandra (CQL) + Neo4j (Cypher) engines
- Add GET /api/sql/catalog/{engine} and GET /api/sql/sample/{engine}
- ssh_terminal: optional initial_command for auto-launching DB CLIs

Frontend:
- DataSourcesView with 5-DB rail, health dots, Browser/Console/Shell sub-tabs
- DbShell embedded xterm terminal with docker exec CLI per engine
- Deep-link topology DB nodes to Data Sources UI (no SQL dock on platform)
- WorkbenchPanel restricted to agent mode only — frees dashboard space

ui/src/App.tsx

@@ -21,6 +21,7 @@ import { DataGenView } from './components/features/DataGenView'
 import { ChangesView } from './components/features/ChangesView'
 import { DataFlowView } from './components/features/DataFlowView'
 import { SearchView } from './components/features/SearchView'
+import { DataSourcesView } from './components/features/DataSourcesView'
 import { SshTerminal } from './components/features/SshTerminal'
 import { TerminalDock } from './components/features/TerminalDock'
 import { WorkbenchPanel } from './components/features/WorkbenchPanel'
@@ -38,6 +39,7 @@ export default function App() {
   const mainScrollRef = useRef<HTMLDivElement>(null)
 
   const isPlatform = cc.mainView === 'platform'
+  const isDataSources = cc.mainView === 'datasources'
 
   const openApprovals = () => {
     cc.setMainView('approvals')
@@ -79,9 +81,9 @@ export default function App() {
           onOpenSsh={() => setSshOpen(true)}
         />
 
-        <div ref={mainScrollRef} className={cn('flex min-h-0 min-w-0 flex-1 flex-col bg-surface', isPlatform ? 'overflow-hidden' : 'scrollbar-thin overflow-y-auto')}>
+        <div ref={mainScrollRef} className={cn('flex min-h-0 min-w-0 flex-1 flex-col bg-surface', (isPlatform || isDataSources) ? 'overflow-hidden' : 'scrollbar-thin overflow-y-auto')}>
           <div className={cn('flex min-h-0 flex-1', isPlatform ? '' : 'flex-col')}>
-            <div className={cn('flex min-h-0 min-w-0 flex-1 flex-col', isPlatform ? 'gap-1 overflow-hidden p-1.5' : 'min-h-0 gap-2 p-3')}>
+            <div className={cn('flex min-h-0 min-w-0 flex-1 flex-col', (isPlatform || isDataSources) ? 'gap-1 overflow-hidden p-1.5' : 'min-h-0 gap-2 p-3')}>
               {isPlatform && (
                 <>
                   <div className="grid shrink-0 grid-cols-1 gap-2 xl:grid-cols-[1fr_auto]">
@@ -119,7 +121,7 @@ export default function App() {
                 </>
               )}
 
-              <div className={cn('flex min-h-0 flex-col', isPlatform ? 'min-h-0 flex-1 overflow-hidden' : 'min-h-0 flex-1')}>
+              <div className={cn('flex min-h-0 flex-col', (isPlatform || isDataSources) ? 'min-h-0 flex-1 overflow-hidden' : 'min-h-0 flex-1')}>
                 {cc.mainView === 'platform' ? (
                   <PlatformTopology
                     workload={cc.workload}
@@ -128,6 +130,8 @@ export default function App() {
                     onNodeClick={cc.selectNode}
                     pulse={cc.genPulse}
                   />
+                ) : cc.mainView === 'datasources' ? (
+                  <DataSourcesView focusEngine={cc.dataSourceFocus} />
                 ) : cc.mainView === 'datagen' ? (
                   <DataGenView onPulse={cc.pulseFlow} onOpenPlatform={() => cc.setMainView('platform')} />
                 ) : cc.mainView === 'changes' ? (