fix(clearance): generate octal squawks and skip reserved codes

genSquawk() drew a decimal number in 1000-8999, so clearances could contain
the digits 8 or 9 — codes no transponder can dial. Replace it with a shared
generateSquawk() that draws four octal digits and re-rolls the reserved codes
(7500/7600/7700, 7000, 2000, 1200, 0000).

shared/learn/scenario.ts had its own octal generator that could still draw an
emergency code; it now uses the same helper.

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

shared/utils/communicationsEngine.ts

@@ -9,6 +9,7 @@ import type {
 } from '../types/decision'
 import type { FlowActivationInstruction, FlowActivationMode, LLMDecisionTrace } from '../types/llm'
 import { normalizeRadioPhrase, DEFAULT_AIRLINE_TELEPHONY } from './radioSpeech'
+import { generateSquawk } from './transponder'
 
 // --- DecisionTree runtime types ---
 type Role = 'pilot' | 'atc' | 'system'
@@ -783,7 +784,7 @@ export default function useCommunicationsEngine() {
             dest: fpl.arr || fpl.arrival || 'EDDM',
             stand: genStand(),
             runway: genRunway(),
-            squawk: fpl.assignedsquawk || genSquawk(),
+            squawk: fpl.assignedsquawk || generateSquawk(),
             atis_code: genATIS(),
             sid: genSID(fpl.route || ''),
             transition: 'DCT',
@@ -1509,10 +1510,6 @@ export default function useCommunicationsEngine() {
         return arr[Math.floor(Math.random() * arr.length)]
     }
 
-    function genSquawk() {
-        return String(Math.floor(Math.random() * 8000 + 1000)).padStart(4, '0')
-    }
-
     function genATIS() {
         const letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
         return letters[Math.floor(Math.random() * letters.length)]