feat(dev): proxy /pb to PocketBase in ng serve

Add proxy.conf.mjs mirroring `location /pb/` from nginx: the prefix is
stripped, target comes from PB_URL (empty value falls back to the default,
same as the SSR provider). Cover the config with tests in tests/lint and
update docs.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

proxy.conf.mjs

@@ -0,0 +1,11 @@
+// @ts-check
+// Повторяет `location /pb/` из docs/architecture.md (раздел 7): только пути с префиксом `/pb/`, префикс срезается.
+// Формат — `server.proxy` dev-сервера Vite (@angular/build).
+/** @type {Record<string, { target: string; changeOrigin?: boolean; rewrite?: (path: string) => string }>} */
+export default {
+    '/pb/': {
+        target: process.env['PB_URL'] || 'http://127.0.0.1:8090',
+        changeOrigin: true,
+        rewrite: (path) => path.replace(/^\/pb/, ''),
+    },
+};