feat: add per-user avatar seed regeneration with irreversible random avatar replacement

Implement a new `avatar_seed` column on the users table that overrides the username-based seed for Multiavatar generation. Introduce a null-safe `avatar_seed(user)` choke point in `avatar.py` that resolves `user.get("avatar_seed") or user.get("username")`, registered as a Jinja global so every render site (`_avatar_link.html`, `avatar_url(...)` calls, SEO `og_image`, issues ad-hoc dicts, devRant payload/PNG) propagates a regenerated seed. Add `POST /profile/{username}/regenerate-avatar` endpoint (owner-or-admin only) that writes a fresh `generate_uid()` to `avatar_seed`, invalidates the target's user cache, and audits `profile.avatar.regenerate`. The previous seed is overwritten and never stored, making regeneration irreversible. Document the feature in `AGENTS.md` and `README.md`, add the API endpoint to `docs_api.py`, and include the `regenerate_avatar` Devii tool in `CONFIRM_REQUIRED`.

tests/api/profile/index.py

@@ -168,3 +168,45 @@ def _seed_feed_posts(count):
 def test_missing_profile_returns_404(app_server):
     r = requests.get(f"{BASE_URL}/profile/no-such-user-xyz", allow_redirects=False)
     assert r.status_code == 404
+
+
+def test_viewing_profile_marks_notification_read(app_server):
+    import time
+    from datetime import datetime, timezone
+    from devplacepy.database import get_table, refresh_snapshot
+    from devplacepy.utils import generate_uid
+
+    name = f"nmark{int(time.time() * 1000)}"
+    session = requests.Session()
+    session.post(
+        f"{BASE_URL}/auth/signup",
+        data={
+            "username": name,
+            "email": f"{name}@t.dev",
+            "password": "secret123",
+            "confirm_password": "secret123",
+        },
+        allow_redirects=True,
+    )
+    refresh_snapshot()
+    user = get_table("users").find_one(username=name)
+    notif_uid = generate_uid()
+    get_table("notifications").insert(
+        {
+            "uid": notif_uid,
+            "user_uid": user["uid"],
+            "type": "follow",
+            "message": "someone followed you",
+            "related_uid": generate_uid(),
+            "target_url": f"/profile/{name}",
+            "read": False,
+            "created_at": datetime.now(timezone.utc).isoformat(),
+        }
+    )
+    refresh_snapshot()
+
+    r = session.get(f"{BASE_URL}/profile/{name}", allow_redirects=True)
+    assert r.status_code == 200
+
+    refresh_snapshot()
+    assert bool(get_table("notifications").find_one(uid=notif_uid)["read"]) is True