feat(server): keep this machine's own settings when importing a database (#6227)

* feat(server): keep this machine's own settings when importing a database

Import replaces the database wholesale, so the uploaded file's listen
addresses, ports, base path, certificate paths and node identity land on the
destination. Moving a configuration to a new host therefore leaves the panel
answering on an address it does not own, presenting certificates it does not
have, and claiming the source machine's identity towards its nodes.

Capture the host-bound settings before the swap and write them back once the
imported database opens. Everything else — inbounds, clients, templates, the
rest of the settings — still comes from the file.

A checkbox controls it, defaulting to keeping this machine's values; clearing
it restores the old behaviour for anyone deliberately cloning a host.

* fix(server): drop imported host settings this machine never had, and cover Postgres

Two gaps in the previous commit. The snapshot only recorded rows that existed,
so a key with no row here — the default for every certificate path, both listen
addresses and all the node mTLS material — kept the imported value: exactly the
case the change is meant to fix. The snapshot now records which keys were
absent and deletes the imported row for them, letting the default apply again.

The PostgreSQL path took the flag and ignored it, so a dump restore still
adopted the source machine's settings. It now captures and restores the same
way the SQLite path does.

* chore: drop the accidentally committed dist build stub

internal/web/dist/.gitkeep is what make dist-stub creates locally. Committing
it changes fresh-clone behaviour for everyone: today a bare go build fails
loudly on //go:embed all:dist, which is the documented signal to run the stub
target; with the file present the build succeeds and the panel serves an empty
dist instead.

---------

Co-authored-by: n0ctal <n0ctal@users.noreply.github.com>
Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

internal/web/translation/ru-RU.json

@@ -266,7 +266,9 @@
       "logLevelError": "Ошибка",
       "accessDirect": "НАПРЯМУЮ",
       "accessBlocked": "ЗАБЛОКИРОВАНО",
-      "accessProxy": "ЧЕРЕЗ ПРОКСИ"
+      "accessProxy": "ЧЕРЕЗ ПРОКСИ",
+      "importKeepHostSettings": "Сохранить настройки этой машины",
+      "importKeepHostSettingsDesc": "Оставляет адреса и порты этой панели, базовый путь, сертификаты и удостоверение для узлов вместо тех, что в загруженном файле."
     },
     "inbounds": {
       "totalDownUp": "Отправлено/получено",