Stop throttling signed media and ease the browser's e621 queue

Signed media URLs are fetched by <img>/<video> tags without an
Authorization header, so they were charged to the anonymous 120/min
bucket: past that, galleries and the fish-greeting download got 429 JSON
instead of image bytes. The raw/thumbnail/staged-file/similarity-file
actions are now exempt, and THROTTLE_ENABLED=false removes the general
anon+user limits for private/tailnet deployments (login/register/proxy
guards stay).

The SPA's e621 client also stops self-throttling so hard: 1s gap between
browsing calls (2.5s for the stricter IQDB endpoint) and a 15s cooldown
instead of 60s when e621 answers 429.

frontend/src/lib/e621.ts

@@ -89,18 +89,19 @@ export function effectiveCredentials(
 const GIT_HASH = typeof __GIT_HASH__ === "string" ? __GIT_HASH__ : "dev";
 const CLIENT_VERSION = `J621/${GIT_HASH} (JakeBreath)`;
 
-// e621 allows 2 requests/second hard, 1/second sustained — and the IQDB
-// endpoint is stricter, so stay comfortably under it. Serialize every request
-// through a queue with a minimum gap.
+// e621 allows 2 requests/second hard, 1/second sustained. Serialize every
+// request through a queue with a minimum gap; IQDB is throttled much harder
+// by e621, so it gets a wider gap of its own.
 let lastRequestAt = 0;
 let queue: Promise<unknown> = Promise.resolve();
 
 /** A hung request would block the whole serialized queue forever. */
 const REQUEST_TIMEOUT_MS = 20_000;
-const REQUEST_GAP_MS = 1500;
+const REQUEST_GAP_MS = 1000;
+const IQDB_GAP_MS = 2500;
 
-/** A 429 (or a CORS-blocked failure) pauses every e621 call for a while. */
-const RATE_LIMIT_COOLDOWN_MS = 60_000;
+/** A 429 (or a CORS-blocked failure) pauses every e621 call briefly. */
+const RATE_LIMIT_COOLDOWN_MS = 15_000;
 const COOLDOWN_KEY = "j621.e621.cooldown";
 let cooldownUntil = 0;
 
@@ -143,10 +144,10 @@ function schedule<T>(task: () => Promise<T>): Promise<T> {
   return run;
 }
 
-async function throttle(): Promise<void> {
+async function throttle(minGap = REQUEST_GAP_MS): Promise<void> {
   const wait = Math.max(
     0,
-    lastRequestAt + REQUEST_GAP_MS - Date.now(),
+    lastRequestAt + minGap - Date.now(),
     e621CooldownRemainingMs(),
   );
   if (wait > 0) {
@@ -168,7 +169,9 @@ export function e621Request<T>(
   options: E621RequestOptions = {},
 ): Promise<T> {
   return schedule(async () => {
-    await throttle();
+    await throttle(
+      path.includes("iqdb_queries") ? IQDB_GAP_MS : REQUEST_GAP_MS,
+    );
 
     const base = credentials.base_url.replace(/\/+$/, "");
     const url = new URL(`${base}/${path.replace(/^\/+/, "")}`);