fix(live-atc): arm the silence timer on readback states too

The timer was only armed for states carrying auto_advance_on_silence. Readback
states carry none — they wait for the pilot — so nothing was armed and ATC
never asked again when the readback did not arrive.

Which window applies to a state is now a pure function: the flow-authored one
for an auto-advance state, the much shorter server-published one for a readback
state. That also makes both cases testable instead of inline in the composable.

tests/shared/silenceTimer.test.ts

@@ -0,0 +1,70 @@
+import { describe, it } from 'node:test'
+import assert from 'node:assert/strict'
+
+import {
+  DEFAULT_READBACK_SILENCE_MS,
+  silenceWindowFor,
+} from '~~/shared/utils/silenceTimer'
+
+describe('silenceWindowFor', () => {
+  it('arms the flow-authored window on an auto-advance state', () => {
+    const window = silenceWindowFor({
+      auto_advance_on_silence: true,
+      auto_advance_timeout_ms: 45000,
+    })
+    assert.deepEqual(window, { kind: 'auto_advance', ms: 45000 })
+  })
+
+  // The bug: a readback state carries no auto_advance_timeout_ms, so nothing
+  // was ever armed and ATC never asked again when the readback did not come.
+  it('arms a readback state, which has no auto-advance window of its own', () => {
+    const window = silenceWindowFor({
+      readback_required: ['squawk', 'sid'],
+      readback_silence_ms: 12000,
+    })
+    assert.deepEqual(window, { kind: 'readback', ms: 12000 })
+  })
+
+  it('chases a missing readback far sooner than an auto-advance', () => {
+    const readback = silenceWindowFor({
+      readback_required: ['runway'],
+      readback_silence_ms: 12000,
+    })!
+    const autoAdvance = silenceWindowFor({
+      auto_advance_on_silence: true,
+      auto_advance_timeout_ms: 45000,
+    })!
+    assert.ok(readback.ms < autoAdvance.ms)
+    assert.ok(readback.ms >= 10_000 && readback.ms <= 15_000, `${readback.ms}ms`)
+  })
+
+  it('falls back to the built-in window when the server published none', () => {
+    const window = silenceWindowFor({ readback_required: ['runway'] })
+    assert.equal(window?.ms, DEFAULT_READBACK_SILENCE_MS)
+  })
+
+  it('arms nothing where the pilot holds the next transmission', () => {
+    assert.equal(silenceWindowFor({}), null)
+    assert.equal(silenceWindowFor({ readback_required: [] }), null)
+    assert.equal(silenceWindowFor(null), null)
+    assert.equal(silenceWindowFor(undefined), null)
+  })
+
+  it('prefers the auto-advance window when a state somehow has both', () => {
+    const window = silenceWindowFor({
+      auto_advance_on_silence: true,
+      auto_advance_timeout_ms: 45000,
+      readback_required: ['runway'],
+      readback_silence_ms: 12000,
+    })
+    assert.equal(window?.kind, 'auto_advance')
+  })
+
+  it('never arms a timer that would fire immediately', () => {
+    assert.equal(silenceWindowFor({ readback_required: ['x'], readback_silence_ms: 0 })?.ms, 1000)
+    assert.equal(
+      silenceWindowFor({ auto_advance_on_silence: true, auto_advance_timeout_ms: -5 })?.ms,
+      1000,
+    )
+  })
+})