feat: schema graph via FK introspection

- GET .../db-connections/:id/foreign-keys — per-dialect
  information_schema/pragma query through dbx_execute_query,
  identifier-whitelisted, read-role gated
- Databases page: Graph tab renders tables as radial SVG nodes with
  FK edges; hover highlights adjacency, click inspects the table
- demo stubs for edges + wider demo table set

Authored By: TDvorak <[email protected]>

packages/api-client/src/generated/schemas/$DBForeignKeyEdge.ts

@@ -0,0 +1,30 @@
+/* generated using openapi-typescript-codegen -- do not edit */
+/* istanbul ignore file */
+/* tslint:disable */
+/* eslint-disable */
+export const $DBForeignKeyEdge = {
+    properties: {
+        schema: {
+            type: 'string',
+        },
+        table: {
+            type: 'string',
+            isRequired: true,
+        },
+        column: {
+            type: 'string',
+            isRequired: true,
+        },
+        ref_schema: {
+            type: 'string',
+        },
+        ref_table: {
+            type: 'string',
+            isRequired: true,
+        },
+        ref_column: {
+            type: 'string',
+            isRequired: true,
+        },
+    },
+} as const;

packages/api-client/src/generated/schemas/$DBForeignKeysResponse.ts

@@ -0,0 +1,21 @@
+/* generated using openapi-typescript-codegen -- do not edit */
+/* istanbul ignore file */
+/* tslint:disable */
+/* eslint-disable */
+export const $DBForeignKeysResponse = {
+    properties: {
+        edges: {
+            type: 'array',
+            contains: {
+                type: 'DBForeignKeyEdge',
+            },
+            isRequired: true,
+        },
+        raw: {
+            type: 'string',
+        },
+        note: {
+            type: 'string',
+        },
+    },
+} as const;