feat: phase 2 databases via DBX (v0.3.0)

- dbx-mcp persistent stdio subprocess in Go backend (internal/dbx),
  lazy start + single retry, tool failures surface as 502
- core.db_connections registry: per-project connections, credentials
  server-side only, managed entries protected (409)
- platform-postgres + platform-dragonfly auto-register per project
- REST proxy: list/create/delete/test, databases, tables, describe,
  schema context, SQL query, redis command
- Databases page: connection list, schema/table browser, column
  inspector, SQL editor with result grid + row detail, redis console
- backend image moved to debian-slim for glibc; pinned dbx release
  with SHA256 verification

Authored By: TDvorak <[email protected]>

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

@@ -0,0 +1,7 @@
+/* generated using openapi-typescript-codegen -- do not edit */
+/* istanbul ignore file */
+/* tslint:disable */
+/* eslint-disable */
+export const $TableQuery = {
+    type: 'string',
+} as const;