App 2.19.7: meter AC charging too, while the app runs

A session runs whenever power flows into the pack, AC or DC; gaps the
head unit slept through are dropped as before. Dashboard and server
texts no longer say DC only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhzAVaUyqcw5PkGjz4mWW6

server/api.go

@@ -15,7 +15,7 @@ import (
 //
 //	POST /v1/telemetry                           live samples, stored
 //	PUT  /v1/consumption/daily                   one delta chunk of a day's consumption
-//	PUT  /v1/charging-sessions/{sessionId}       one finished DC charging session
+//	PUT  /v1/charging-sessions/{sessionId}       one finished charging session (AC or DC)
 //	GET  /v1/consumption/history/{installationId} the car reads its own totals back
 //	GET  /v1/health                              unauthenticated liveness probe
 //	     /v1/settings/…, /settings                settings typed on a phone (handoff_http.go)