add migration page

docs/config-migration-standalone.md

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+# Migration to Standalone Rewrite Config
+
+This page compares the legacy AppDaemon `apps.yaml` config with the standalone rewrite `panels.yaml` config.
+
+For the full rewrite docs, including full key descriptions, see:
+
+- [Standalone documentation](https://docs.nspanel.pky.eu/standalone/)
+- [Standalone migration page](https://docs.nspanel.pky.eu/standalone/migration-appdaemon/)
+
+## High-level differences
+
+Old AppDaemon version:
+
+- panel config in `apps.yaml` with `module` / `class` / `config`
+- connectivity partly configured in AppDaemon plugin config (`appdaemon.yaml`)
+
+Standalone rewrite:
+
+- one runtime config file: `/config/panels.yaml`
+- panel definitions under `nspanels`
+- Home Assistant and MQTT connection values resolved directly by the rewrite runtime
+
+## Minimal before/after example
+
+Old (`apps.yaml`):
+
+```yaml
+nspanel-1:
+  module: nspanel-lovelace-ui
+  class: NsPanelLovelaceUIManager
+  config:
+    panelRecvTopic: "tele/tasmota_panel/RESULT"
+    panelSendTopic: "cmnd/tasmota_panel/CustomSend"
+    model: eu
+```
+
+New (`panels.yaml`):
+
+```yaml
+home_assistant_address: "http://supervisor"
+home_assistant_token: "YOUR_TOKEN"
+
+nspanels:
+  panel-1:
+    panelRecvTopic: "tele/tasmota_panel/RESULT"
+    panelSendTopic: "cmnd/tasmota_panel/CustomSend"
+    model: eu
+    locale: en_US
+    timeZone: "Europe/Berlin"
+    timeFormat: "%H:%M"
+    dateFormat: "full"
+    screensaver:
+      entities:
+        - entity: weather.home
+    cards:
+      - type: cardEntities
+        title: Main
+        entities:
+          - entity: light.kitchen
+```
+
+## Important key changes
+
+Legacy key/concept | Rewrite key/concept | Notes
+-- | -- | --
+`module`, `class`, `config` wrapper | removed | Rewrite uses `nspanels.<panel_name>` directly.
+`timezone` | `timeZone` | Casing changed.
+`dateFormatBabel` | `dateFormat` | Use `dateFormat` in rewrite.
+`temperatureUnit` (legacy card-level usage) | `temp_unit` (panel-level) | Rewrite reads `temp_unit` from panel settings.
+brightness schedule lists | not supported | Rewrite supports integer or entity id for brightness values.
+`updateMode` / OTA URL override keys | not supported | Legacy update behavior is not part of rewrite config.
+
+If you are migrating now, use the standalone migration page for the complete mapping:
+
+- [Complete mapping and checklist](https://docs.nspanel.pky.eu/standalone/migration-appdaemon/)