refactor(live-atc): extract normalizeManualFreq to shared/utils, add tests

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/shared/frequency.test.ts

@@ -0,0 +1,26 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { normalizeManualFreq } from '../../shared/utils/frequency.ts'
+
+test('normalizeManualFreq pads a bare integer to three decimals', () => {
+  assert.equal(normalizeManualFreq('121'), '121.000')
+})
+
+test('normalizeManualFreq accepts a comma decimal separator', () => {
+  assert.equal(normalizeManualFreq('121,3'), '121.300')
+})
+
+test('normalizeManualFreq rejects values outside the VHF airband', () => {
+  assert.equal(normalizeManualFreq('99.000'), null)
+  assert.equal(normalizeManualFreq('110.000'), null)
+  assert.equal(normalizeManualFreq('140.000'), null)
+})
+
+test('normalizeManualFreq accepts the lower airband boundary', () => {
+  assert.equal(normalizeManualFreq('118'), '118.000')
+})
+
+test('normalizeManualFreq rejects garbage input', () => {
+  assert.equal(normalizeManualFreq('abc'), null)
+  assert.equal(normalizeManualFreq(''), null)
+})