feat(diagnostics): 'playback' kind, newest-first sort, fix active-route subtitle

Relabel (#1204): route + player_state events fire for every output route,
not just UPnP — split them into a new 'playback' kind; 'upnp_sync' now
means genuinely UPnP/Sonos signal (drops, resync). Migration 0037 adds
'playback' to the kind CHECK; server whitelist, Android reporter labels,
and the web kind filter updated.

Web sort: the diagnostics list gains a Newest/Oldest-first sort (default
newest at top); export follows the displayed order.

Fix (#1205): OutputRoute.isConnected was derived from RouteInfo.connectionState,
which stays DISCONNECTED for local SYSTEM routes even when active — so a
connected Bluetooth device showed "Available" and reported connected:false.
The picker subtitle now uses isSelected (route == selected route); the dead
isConnected field is removed and the misleading `connected` field dropped
from the diagnostics route event (it only ever logs the active route).

Refs Scribe M9 (#119), tasks #1204 #1205.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K55iTxn95BtshocgdE1shW

internal/api/diagnostics.go

@@ -21,7 +21,8 @@ import (
 // variants do NOT require a new category here.
 var validDiagnosticKinds = map[string]struct{}{
 	"connectivity": {},
-	"upnp_sync":    {},
+	"upnp_sync":    {}, // genuinely UPnP/Sonos-specific (drops, resync)
+	"playback":     {}, // route + player-state, any output (phone/BT/UPnP)
 	"power":        {},
 	"lifecycle":    {},
 	"heartbeat":    {},