Add a blacklist editor that saves to e621

The Online sidebar's "Your blacklist" section is editable now: typing a
tag appends it and each entry gets an x to remove it. Changes are written
straight to the e621 account (PATCH /users/{id}.json with
user[blacklisted_tags]); the store keeps the fetched profile for the id,
updates the list optimistically and reloads it from e621. The Followed
page's blacklist cloud is rebuilt afterwards via the new
/api/follows/cloud/?refresh=1 force flag.

Verified against the live API with a reversible add/verify/restore test.

frontend/src/lib/e621.ts

@@ -316,6 +316,18 @@ export async function fetchPostsByMd5(
   return data.posts;
 }
 
+/** Replace the account's blacklist (e621 stores it as one newline-joined string). */
+export async function updateBlacklist(
+  credentials: E621Credentials,
+  userId: number,
+  blacklist: string,
+): Promise<void> {
+  await e621Request(credentials, `/users/${userId}.json`, {
+    method: "PATCH",
+    body: new URLSearchParams({ "user[blacklisted_tags]": blacklist }),
+  });
+}
+
 export interface E621Pool {
   id: number;
   name: string;