fix(types): bring real code to zero TypeScript errors, fix three latent bugs

Continues the cleanup from 164 errors down to 88, all of which now sit in
MemStorage — the in-memory dev mock — documented as known debt. Production
server code and the entire client are at zero errors.

Three genuine defects surfaced by the types and fixed:
- deleteAnnouncement returned void while routes check the result and answer
  404 "not found" on falsy: deleting an announcement succeeded in DB but the
  API reported failure on the fallback paths; it now returns a real boolean
- AnnouncementMemoryStorage declared getAnnouncement twice; the first
  implementation was dead at runtime (second definition wins) and is removed
- one route called storage.getDeliveryById(), a method that does not exist,
  crashing with a TypeError whenever hit; it now calls getDelivery()

Everything else is type-level only (annotations, null-to-undefined for
inline styles, honest signatures for markClientCalled's comment parameter
and the invoice verification result's invoiceAmountTTC field), verified
behavior-neutral: client build, production server bundle and the SMTP
end-to-end test all pass unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FHdE9nEh8zHhQNGpCgrtYe

server/cache.ts

@@ -93,7 +93,7 @@ export function invalidateCache(pattern: string): void {
 export function setupCompression(app: any) {
   app.use((req: Request, res: Response, next: NextFunction) => {
     // Activer la compression pour les réponses JSON
-    if (req.accepts('gzip') && res.getHeader('Content-Type')?.includes('json')) {
+    if (req.accepts('gzip') && String(res.getHeader('Content-Type') ?? '').includes('json')) {
       res.setHeader('Content-Encoding', 'gzip');
     }
     next();