feat: Gravatar opt-in (off by default), configurable in Settings

Previously every account without a custom avatar automatically got
its email MD5-hashed and sent to gravatar.com at signup, with no way
to turn it off. Adds users.useGravatar (default false): removed the
automatic signup-time lookup entirely, and "remove photo" now falls
back to the initials placeholder instead of silently re-deriving a
Gravatar URL. New toggle in Settings -> Profile, off by default,
description explains the MD5-hash-to-third-party tradeoff. Existing
accounts' current avatarUrl is left untouched either way — no
retroactive avatar changes for anyone already using one.

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

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.24.1";
+export const APP_VERSION = "0.25.0";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.25.0",
+    date: "2026-07-14 09:36",
+    added: [
+      "**Gravatar is now opt-in, off by default** — previously every account without a custom photo automatically had its email hashed and sent to gravatar.com. Turn it on in Settings → Profile if you want it.",
+    ],
+  },
   {
     version: "0.24.1",
     date: "2026-07-14 09:24",