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":    {},

internal/db/migrations/0037_diagnostics_playback_kind.down.sql

@@ -0,0 +1,9 @@
+-- Drop rows using the new value first so they don't violate the restored
+-- (narrower) constraint, then revert the whitelist.
+DELETE FROM diagnostic_events WHERE kind = 'playback';
+ALTER TABLE diagnostic_events DROP CONSTRAINT diagnostic_events_kind_check;
+ALTER TABLE diagnostic_events ADD CONSTRAINT diagnostic_events_kind_check
+    CHECK (kind IN (
+        'connectivity', 'upnp_sync', 'power', 'lifecycle',
+        'heartbeat', 'http'
+    ));

internal/db/migrations/0037_diagnostics_playback_kind.up.sql

@@ -0,0 +1,19 @@
+-- Add 'playback' to the diagnostic_events kind whitelist (M9 follow-up).
+--
+-- `route` and `player_state` events fire for EVERY output route (phone
+-- speaker, Bluetooth, UPnP/Sonos), so bucketing them under 'upnp_sync'
+-- was misleading — an operator on Bluetooth earbuds saw "upnp_sync"
+-- rows. 'upnp_sync' now means genuinely UPnP/Sonos-specific signal
+-- (drops, and future resync/desync); general playback + route telemetry
+-- moves to the new 'playback' kind.
+--
+-- Per the enum-CHECK-whitelist rule, the new value lands by dropping and
+-- re-adding the constraint in the same change. Existing rows tagged
+-- 'upnp_sync' stay as-is (debug telemetry on a 30-day retention).
+
+ALTER TABLE diagnostic_events DROP CONSTRAINT diagnostic_events_kind_check;
+ALTER TABLE diagnostic_events ADD CONSTRAINT diagnostic_events_kind_check
+    CHECK (kind IN (
+        'connectivity', 'upnp_sync', 'power', 'lifecycle',
+        'heartbeat', 'http', 'playback'
+    ));