Add backlog tasks and launcher time helper tests

- Track follow-up cleanup work in Backlog.md
- Replace Date.now usage with shared nowMs helper
- Add launcher args/parser and core regression tests

launcher/commands/playback-command.ts

@@ -14,6 +14,7 @@ import {
   waitForUnixSocketReady,
 } from '../mpv.js';
 import type { Args } from '../types.js';
+import { nowMs } from '../time.js';
 import type { LauncherCommandContext } from './context.js';
 import { ensureLauncherSetupReady } from '../setup-gate.js';
 import {
@@ -116,7 +117,7 @@ async function ensurePlaybackSetupReady(context: LauncherCommandContext): Promis
       child.unref();
     },
     sleep: (ms) => new Promise((resolve) => setTimeout(resolve, ms)),
-    now: () => Date.now(),
+    now: () => nowMs(),
     timeoutMs: SETUP_WAIT_TIMEOUT_MS,
     pollIntervalMs: SETUP_POLL_INTERVAL_MS,
   });

launcher/commands/stats-command.ts

@@ -2,6 +2,7 @@ import fs from 'node:fs';
 import os from 'node:os';
 import path from 'node:path';
 import { runAppCommandAttached } from '../mpv.js';
+import { nowMs } from '../time.js';
 import { sleep } from '../util.js';
 import type { LauncherCommandContext } from './context.js';
 
@@ -45,8 +46,8 @@ const defaultDeps: StatsCommandDeps = {
   runAppCommandAttached: (appPath, appArgs, logLevel, label) =>
     runAppCommandAttached(appPath, appArgs, logLevel, label),
   waitForStatsResponse: async (responsePath, signal) => {
-    const deadline = Date.now() + STATS_STARTUP_RESPONSE_TIMEOUT_MS;
-    while (Date.now() < deadline) {
+    const deadline = nowMs() + STATS_STARTUP_RESPONSE_TIMEOUT_MS;
+    while (nowMs() < deadline) {
       if (signal?.aborted) {
         return {
           ok: false,