feat: live expected communication from backend, radio pronunciation toggle, and frequency validation

- Expected Communication card now driven entirely by backend responses:
  controller speech from controller_say_rendered, expected pilot phrase
  from expected_pilot_template — both update after every state transition
  instead of relying on the static COMMUNICATION_STEPS array
- Initial expected pilot phrase seeded on session creation via the new
  expected_pilot_template field in CreateSessionResponse, so the card
  shows the correct text before any transmission
- Radio pronunciation toggle (mdi-radio / mdi-text) on the card applies
  normalizeRadioPhrase() (ICAO alphabet, wun/too/tree, callsign expansion)
  to both ATC speech and expected pilot phrase
- Frequency validation at transmit time: if the pilot's active frequency
  does not match the state's expected frequency (resolved from
  frequency_name → flight-plan variable) a canned ATC reply is played
  and the backend is not called
- Flight-plan variables (callsign, squawk, destination, ATIS, SID, stand,
  initial altitude) now passed to createSession() as variable_overrides
  so backend sessions use real flight-plan data from the first state
- Backend session variables synced into local vars after each response
  so frontend and backend stay consistent
- Removed hardcoded frequency chip from Expected Communication card

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/composables/useRadioBackend.ts

@@ -4,6 +4,7 @@ export interface RadioSessionResponse {
     current_state: string
     variables: Record<string, any>
     flags: Record<string, boolean>
+    expected_pilot_template: string | null
 }
 
 export interface RadioTransmitResponse {
@@ -27,10 +28,13 @@ export function useRadioBackend() {
         return (config.public.radioBackendUrl as string) || 'http://127.0.0.1:8000'
     }
 
-    async function createSession(flowSlug: string): Promise<RadioSessionResponse> {
+    async function createSession(
+        flowSlug: string,
+        variables?: Record<string, any>,
+    ): Promise<RadioSessionResponse> {
         return await $fetch<RadioSessionResponse>(`${baseUrl()}/api/radio/session`, {
             method: 'POST',
-            body: { flow_slug: flowSlug },
+            body: { flow_slug: flowSlug, variables: variables ?? null },
         })
     }