Timed fades, mute-style matrix sends, meters on matrix send knobs

- Every set-level action (input, bus, matrix and control group faders,
  aux and matrix sends) has a fade time and a curve: fader travel
  (natural), fader travel with ease in/out, or linear in dB. Fades step
  at 20 Hz, land exactly on the target, never overshoot, and are
  cancelled by any new move on the same fader; new "Stop all fades"
  action, fades_running variable and fade_running feedback. Verified on
  the S31 with a switched-off matrix send: 20 writes in 1 s, ending
  exactly on target, then restored.
- Matrix sends now look like mutes in the presets: red when the send is
  off, black when it is on (new matrix_send_off feedback, true only when
  the send is known to be off).
- Matrix send knobs carry a meter column on the right. The S31 has no
  meter for matrix inputs, so it shows the destination output's meter.
  Meter gauges use a faint track so an empty meter reads as empty.
- Test fixes: the meter-resubscribe check no longer depends on a silent
  channel changing value, plus back-to-back /Meters/clear coverage.

npm test: 504 checks pass on Node 25 and on Companion's Node 22.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/definitions/variables.js

@@ -30,6 +30,7 @@ export function getVariableDefinitions(inst) {
 		connected: { name: 'Console link alive (Yes/No)' },
 		relay_clients: { name: 'iPad apps connected through the relay' },
 		relay_client_ips: { name: 'iPad client IPs' },
+		fades_running: { name: 'Number of level fades running' },
 		last_change: { name: 'Last change reported by the console' },
 		snapshot_index: { name: 'Current snapshot index' },
 		snapshot_name: { name: 'Current snapshot name' },
@@ -75,7 +76,7 @@ export function snapshotVariableValues(inst) {
 /** Everything, after the definitions were rebuilt. */
 export function getAllVariableValues(inst) {
 	const s = inst.state
-	const out = { console_name: s.console.name, session_name: s.console.session, connected: inst.connectedFlag ? 'Yes' : 'No', ...snapshotVariableValues(inst) }
+	const out = { console_name: s.console.name, session_name: s.console.session, connected: inst.connectedFlag ? 'Yes' : 'No', fades_running: inst.fades?.size ?? 0, ...snapshotVariableValues(inst) }
 	for (const ent of Object.keys(ENTITY_VARS)) for (const n of s.numbers(ent)) Object.assign(out, entityVariableValues(inst, ent, n))
 	return out
 }