feat: add multi-device provisioning and local remote-config UI

- add multi-device portal device management, key rotation, and sync request APIs
- add Pi settings UI for remote server URL, device name, and API key
- add local test-connection and sync-now actions
- make upload and config sync reuse dynamic shared credentials
- add Phase 25.5c migration and docs updates

Co-authored-by: Copilot <[email protected]>

readme.md

@@ -59,11 +59,12 @@ Dashboard — mobile (390 px) and desktop (1280 px):
   trip history with OSM/CARTO live map and route replay, dashcam archive browsing with inline
   video player and Range-request seeking, overview stats dashboard, delete buttons for trips and
   clips, and a device-settings page for editing the synced owner/car/avatar values that the Pi
-  pulls from the server. When the Pi has **Sync with server** enabled, those identity changes hot-
-  reload into the running local UI on the next successful sync instead of waiting for a manual
-  restart. Shared `history.js` code runs on both the Pi and the server — tile
-  source and zoom limits are configured per-deployment via HTML data attributes. Accessible at
-  `https://your-cloudflare-tunnel-url/`
+  pulls from the server. The portal can register multiple devices, reveal a one-time API key at
+  creation/rotation time, and request a sync for a selected device. When the Pi has
+  **Sync with server** enabled, those identity changes hot-reload into the running local UI on the
+  next successful sync instead of waiting for a manual restart. Shared `history.js` code runs on
+  both the Pi and the server — tile source and zoom limits are configured per-deployment via HTML
+  data attributes. Accessible at `https://your-cloudflare-tunnel-url/`
 - 📡 **Optional cellular fallback** through the SIM868 for small trip-log uploads when normal
   WiFi/Ethernet is unavailable (dashcam video stays off cellular)
 - 🗄️ **Motion-aware local-first SQLite logging** — five-second motion checks without five-second