feat: odometer baseline syncs to server — push on save, pull on sync, +/api/device-config/push endpoint

server/sql/migrate_phase27_odometer.sql

@@ -0,0 +1,2 @@
+-- Phase 27: Add odometer_baseline to devices table for server-side sync.
+ALTER TABLE devices ADD COLUMN IF NOT EXISTS odometer_baseline DOUBLE PRECISION NOT NULL DEFAULT 0;