chore+fix: repo hygiene, code-review fixes, audit cleanup

Three independent code reviews + a security audit produced ~200 findings.
This commit lands the high-impact subset. Tests pass (53), typecheck
clean, eslint clean (3 minor exhaustive-deps warnings left).

REPO HYGIENE
- Add .editorconfig, .prettierrc.json, .prettierignore.
- Add ESLint flat config (.eslintrc.cjs) — correctness-focused, no style
  rules (Prettier owns formatting).
- Add `format` / `format:check` / `lint` npm scripts.
- Add CHANGELOG.md (Keep a Changelog format, back-filled to 0.1.x).
- Reformat all source via Prettier so future diffs stay small.

DATA SAFETY (src/main/store.ts)
- Atomic write (tmp + rename) with retry on transient EBUSY/EPERM —
  was non-atomic writeFileSync, vulnerable to truncation on power loss.
- On corrupt JSON, rename to `app-state.json.corrupt-<ts>` instead of
  silently overwriting the user's exercises/history with defaults.
- Validate parsed shape before merging — reject arrays/scalars where
  objects expected; per-field array checks.
- Strip `id` from incoming patches in updateExercise/updateChallenge —
  a runtime caller (IPC) could otherwise smuggle id changes through.
- clearHistory now refuses an unbounded wipe (no beforeTs => no-op);
  callers must pass an explicit boundary.
- unref() the debounce timer so it doesn't keep the event loop alive.

SECURITY (src/main/*)
- gsi-server: hard 256 KB body cap (was unbounded — local OOM vector),
  reject any Origin/Sec-Fetch-Site header (blocks browser CSRF from
  visited pages), require application/json Content-Type, generic 400
  on parse error (no error string echo to client), closeAllConnections
  + async close on stop.
- dota2: validate auth.token from payload with timingSafeEqual against
  the per-install token — was unauthenticated, any local process could
  forge match-end events. Narrow object shape before spread-merge to
  avoid throws on hostile payloads like {player:"x"}. Reset latest /
  prevState after match_end so the next match starts clean.
- ipc: gate `dev:simulateMatchEnd` registration behind `!app.isPackaged`
  so it does not exist in shipped builds.
- preload: gate the matching `simulateMatchEnd` export behind
  `import.meta.env.MODE !== 'production'` so the bundler dead-code-
  eliminates it from the production preload bundle.
- windows: shell.openExternal allowlist (http/https/mailto only) — was
  forwarding any URL, including file:/javascript:/custom URI handlers
  (some Windows handlers have been RCE vectors). will-navigate blocks
  navigation to anywhere except file:// or the dev URL.

CORRECTNESS (src/main/* + src/shared/*)
- shared/types.ts isQuietAt: fix wrap-around + day-of-week filter.
  With from=22:00 to=07:00 days=[Mon..Fri], the window started THE
  PREVIOUS DAY when we're in the AM half — old code checked today's
  day-of-week and got the wrong answer Sat 02:00 and Mon 01:00. Now
  the filter is evaluated against the window's START day. Also reject
  malformed HH:MM strings instead of producing NaN.
- scheduler: call broadcastState() after firing exercises so the
  renderer's Dashboard/Exercises pages don't show stale nextFireAt
  until the next state-changing IPC. Guard powerMonitor listeners
  against double-registration on dev hot-reload.
- dota2: fix `launchOptionStatus = steamRunning ? 'queued' : 'queued'`
  tautology — both branches now correctly read 'queued'.
- steam-launch-options: replace `require('node:fs')` inside atomicWrite
  with the top-level import; retry on transient EBUSY/EPERM.

CORRECTNESS (src/renderer/*)
- lib/history.ts: replace `today.getTime() - i * MS_DAY` arithmetic
  with `setDate(date - i)` calendar arithmetic in dailyRepsRange and
  currentStreak — DST transitions shift epoch math by ±1h and cause
  dayKey() to emit duplicate or missing days at the boundary.
- lib/icon.tsx: restrict name lookup to ICON_CHOICES set — an arbitrary
  string from a corrupted state file could otherwise resolve to
  unrelated Lucide exports and crash the renderer.
- lib/format.ts: guard formatCountdown against NaN/Infinity.
- i18n/index.ts: replace regex-based interpolation with split/join so
  variable values containing regex metacharacters interpolate
  literally; warn in dev on missing keys; clamp pluralRu(-N) via abs.
- ReminderApp: keyboard shortcuts moved INTO ExerciseReminder so Enter
  respects the stepper's `adjusted` flag (was always passing planned
  reps). Stepper capped at 5× planned. Don't hijack Space when a
  button is focused. `key={exercise.id+nextFireAt}` forces a fresh
  component for back-to-back reminders so stepper state resets. Match
  summary view gets Esc-to-close. Functional setMode in onMarkDone
  avoids races against stale `mode.done`.
- UpdaterCard: guard against NaN/Infinity in download-progress events
  (electron-updater fires early events with undefined fields).
- Games: gate DevPanel behind `import.meta.env.DEV` in addition to the
  main-side IPC gate, and narrow the `simulateMatchEnd` access.
- Add aria-labels for the +/- stepper buttons (i18n keys added).

TESTS
- +2 quiet-hours tests covering wrap-around + day-filter combo and
  malformed HH:MM fallback. Total 53 passing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/main/scheduler.ts

@@ -4,10 +4,17 @@ import type { Tick } from '@shared/types'
 import { isQuietAt } from '@shared/types'
 import { getExercises, getSettings, updateExercise } from './store'
 import { fireReminder } from './notifications'
+import { broadcastState } from './state-actions'
 
+/**
+ * TICK_MS drives the per-second countdown UI; CHECK_MS gates the (cheaper)
+ * "is anything due to fire?" pass so we don't iterate exercises every second.
+ */
 const TICK_MS = 1000
 const CHECK_MS = 5000
+
 let tickHandle: NodeJS.Timeout | null = null
+let powerListenersArmed = false
 let lastCheckAt = 0
 let paused = false
 
@@ -16,21 +23,28 @@ function checkDueExercises(): void {
   const settings = getSettings()
   if (!settings.globalEnabled) return
 
-  // Inside the quiet window: defer all due fires to the next minute boundary.
-  // The next tick after the window closes will pick them up.
+  // Inside the quiet window: defer all due fires until it closes. The next
+  // CHECK_MS pass after the window ends will pick them up.
   if (isQuietAt(settings.quietHours, new Date())) return
 
   const now = Date.now()
   const exercises = getExercises()
+  let anyFired = false
   for (const ex of exercises) {
     if (!ex.enabled) continue
     if (ex.nextFireAt <= now) {
       const updated = updateExercise(ex.id, {
         nextFireAt: now + ex.intervalMinutes * 60_000
       })
-      if (updated) fireReminder(updated, settings.notificationMode)
+      if (updated) {
+        anyFired = true
+        fireReminder(updated, settings.notificationMode)
+      }
     }
   }
+  // Push fresh state so the renderer's Dashboard/Exercises pages don't show
+  // stale `nextFireAt` until the next state-changing IPC arrives.
+  if (anyFired) broadcastState()
 }
 
 function broadcastTicks(): void {
@@ -61,14 +75,20 @@ export function startScheduler(): void {
   // Run an immediate tick so renderer hydrates quickly.
   tick()
 
-  powerMonitor.on('resume', () => {
-    lastCheckAt = 0
-    tick()
-  })
-  powerMonitor.on('unlock-screen', () => {
-    lastCheckAt = 0
-    tick()
-  })
+  // Only attach powerMonitor listeners once per process — startScheduler may
+  // be invoked again after stopScheduler in dev hot-reload paths and we don't
+  // want the same handler firing N times after a resume.
+  if (!powerListenersArmed) {
+    powerListenersArmed = true
+    powerMonitor.on('resume', () => {
+      lastCheckAt = 0
+      tick()
+    })
+    powerMonitor.on('unlock-screen', () => {
+      lastCheckAt = 0
+      tick()
+    })
+  }
 }
 
 export function stopScheduler(): void {