fix(ingress): refuse hostile bytes before the disabled-model shortcut (#16)

The release builder runs its browser gates with TIMMY_VISION_ENABLED=false, and
the 503 "AI analysis is disabled" branch ran before the request budget, body
limits, and byte-level ingress guard. Under builder conditions every hostile
upload answered 503, so the refusal boundary was never exercised and the
ingress-capture gate this same PR added failed:

  AssertionError: the server must refuse non-image bytes, saw 503

Refusals now run in cost order regardless of model availability: budget, body,
bytes, then the disabled switch. Verified with vision disabled: hostile bytes
-> 400 not_an_image, a valid synthetic photo -> 503 with the existing copy.
npm test 277 pass; ingress-capture and the other browser gates green under the
builder's env.

server.mjs

@@ -76,8 +76,9 @@ http.createServer(async(req,res)=>{
    return sendJson(res,200,{...visionConfig.publicStatus(),providerReady:provider.ready,modelSeen:provider.modelSeen,privacy});
   }
   if(appPath==='/api/analyze'&&req.method==='POST'){
-   if(!visionConfig.enabled)return sendJson(res,503,{error:'AI analysis is disabled. Continue manually.'});
-   // Cheap refusals first, in cost order: the request budget, then the body, then the image itself.
+   // Refusals first, in cost order: the request budget, then the body, then the image bytes. None of
+   // these depend on the model, so hostile bytes are refused as hostile even when analysis is off —
+   // otherwise the disabled switch hides the ingress boundary behind a 503 and the refusal is untested.
    const budget=analyzeLimiter.take(clientBucket(req));
    if(!budget.allowed){
     res.setHeader('retry-after',String(Math.max(1,Math.ceil(budget.retryAfterMs/1000))));
@@ -94,6 +95,8 @@ http.createServer(async(req,res)=>{
    }
    try{ingressGuard(payload)}
    catch(error){return sendIngressError(res,error)}
+   // Bytes are known to be a real photo at this point, so the disabled switch is the honest answer.
+   if(!visionConfig.enabled)return sendJson(res,503,{error:'AI analysis is disabled. Continue manually.'});
    try{return sendJson(res,200,await analyzePhoto({payload,config:visionConfig}))}
    catch(error){const failure=visionFailureResponse(error);return sendJson(res,failure.status,failure.body)}
   }