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]>

server/sql/init.sql

@@ -8,7 +8,17 @@ CREATE TABLE IF NOT EXISTS devices (
     name          TEXT NOT NULL UNIQUE,          -- e.g. "yaris-2013"
     api_key_hash  TEXT NOT NULL,                 -- sha256 hex digest of the device's API key, never the raw key
     created_at    TIMESTAMPTZ NOT NULL DEFAULT now(),
-    last_seen_at  TIMESTAMPTZ
+    last_seen_at  TIMESTAMPTZ,
+    owner_name    TEXT DEFAULT '',
+    car_model     TEXT DEFAULT '',
+    device_name   TEXT DEFAULT '',
+    avatar_path   TEXT DEFAULT 'img/yaris.png',
+    config_version INTEGER NOT NULL DEFAULT 0,
+    config_updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    last_config_sync_at TIMESTAMPTZ,
+    last_config_sync_version INTEGER,
+    force_sync_requested_at TIMESTAMPTZ,
+    api_key_rotated_at TIMESTAMPTZ
 );
 
 CREATE TABLE IF NOT EXISTS tracking_points (