fix(live-atc): match the D-registration to the aircraft class

VFR scenarios drew from a fixed pool of D-E** registrations regardless of type,
so an A320 was assigned "D-ETMO". The letter after "D-" is assigned by weight
and type class (LuftVZO Anlage 1): D-E is single-engine pistons up to 2 t, so
an airliner has to be D-A.

Pick the class from the ICAO type designator — D-A for airliners, D-I for light
twins, D-H for helicopters, D-E for light singles and anything unrecognised,
since VFR scenarios are overwhelmingly light aircraft.

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

shared/utils/registration.ts

@@ -0,0 +1,89 @@
+/**
+ * German aircraft registrations (D-…).
+ *
+ * The letter after "D-" is not decorative: LuftVZO Anlage 1 assigns it by
+ * weight and type class, so a registration has to match the aircraft. D-E is
+ * reserved for single-engine pistons up to 2 t — an A320 wearing one is as
+ * wrong as an airliner with a glider's callsign.
+ *
+ *   D-A…  above 20 t (airliners)
+ *   D-I…  multi-engine piston, 2–5.7 t
+ *   D-E…  single-engine piston, up to 2 t
+ *   D-H…  helicopters
+ */
+
+export type RegistrationPrefix = 'A' | 'I' | 'E' | 'H'
+
+/** ICAO type designators that are not light singles, by registration class. */
+const TYPES_BY_PREFIX: Record<Exclude<RegistrationPrefix, 'E'>, ReadonlySet<string>> = {
+    A: new Set([
+        // Narrowbody / widebody / regional jets — all comfortably above 20 t.
+        'A318', 'A319', 'A320', 'A321', 'A20N', 'A21N',
+        'A332', 'A333', 'A339', 'A342', 'A343', 'A345', 'A346',
+        'A359', 'A35K', 'A388',
+        'B733', 'B734', 'B735', 'B736', 'B737', 'B738', 'B739',
+        'B37M', 'B38M', 'B39M',
+        'B752', 'B753', 'B762', 'B763', 'B764',
+        'B772', 'B773', 'B77L', 'B77W', 'B788', 'B789', 'B78X',
+        'B742', 'B744', 'B748',
+        'E170', 'E175', 'E190', 'E195', 'E290', 'E295',
+        'CRJ2', 'CRJ7', 'CRJ9', 'CRJX',
+        'AT72', 'AT76', 'DH8D', 'BCS1', 'BCS3', 'SU95',
+    ]),
+    I: new Set([
+        // Multi-engine pistons in the 2–5.7 t band.
+        'BE58', 'BE55', 'BE76', 'BE60', 'BE95',
+        'PA34', 'PA31', 'PA44', 'PA23',
+        'C310', 'C320', 'C337', 'C340', 'C402', 'C404', 'C414', 'C421',
+        'DA62', 'P68', 'AC11', 'AC50',
+    ]),
+    H: new Set([
+        'R22', 'R44', 'R66', 'EC20', 'EC30', 'EC35', 'EC45', 'EC55',
+        'H125', 'H130', 'H135', 'H145', 'AS50', 'AS55', 'AS65',
+        'B06', 'B06T', 'B407', 'B429', 'S76', 'A109', 'A139', 'MD90',
+    ]),
+}
+
+/**
+ * Pools of pronounceable registrations per class. Real German registrations
+ * read as words on the radio, which matters because these are spoken by TTS
+ * and transcribed back from the pilot.
+ */
+const REGISTRATION_POOLS: Record<RegistrationPrefix, readonly string[]> = {
+    A: ['D-AIZA', 'D-AIBL', 'D-ABYT', 'D-AIMA', 'D-AINK', 'D-ABKM', 'D-AIDF', 'D-ACNL'],
+    I: ['D-IBSL', 'D-IAAB', 'D-IHAG', 'D-IFOX', 'D-IKMR', 'D-IWAL'],
+    E: ['D-EMIL', 'D-EKLM', 'D-ENNY', 'D-ELLA', 'D-EOMT', 'D-ELPC', 'D-EMTO', 'D-EBRA'],
+    H: ['D-HAFH', 'D-HBKD', 'D-HELI', 'D-HMUC', 'D-HAXE', 'D-HRTG'],
+}
+
+/**
+ * Registration class letter for an ICAO type designator.
+ *
+ * Unknown types fall back to the light-single class: these registrations are
+ * assigned in VFR scenarios, which are overwhelmingly light aircraft.
+ */
+export function germanRegistrationPrefix(aircraftType: string): RegistrationPrefix {
+    // Flight plans carry things like "A320/M" or "C172 " — keep the designator.
+    const type = (aircraftType || '').trim().toUpperCase().split(/[/\s-]/)[0] || ''
+    if (!type) return 'E'
+
+    for (const prefix of ['A', 'I', 'H'] as const) {
+        if (TYPES_BY_PREFIX[prefix].has(type)) return prefix
+    }
+    return 'E'
+}
+
+export interface GermanRegistration {
+    /** Full registration, e.g. "D-EMIL". */
+    registration: string
+    /** Abbreviated form German ATC uses after first contact, e.g. "D-IL". */
+    short: string
+}
+
+/** A registration whose class matches the aircraft type. */
+export function generateGermanRegistration(aircraftType: string): GermanRegistration {
+    const pool = REGISTRATION_POOLS[germanRegistrationPrefix(aircraftType)]
+    const registration = pool[Math.floor(Math.random() * pool.length)]!
+    // ATC abbreviates to the first character and the last two: D-EMIL → D-IL.
+    return { registration, short: `D-${registration.slice(-2)}` }
+}