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`.

devplacepy/routers/devii.py

@@ -8,7 +8,7 @@ from fastapi.responses import JSONResponse, RedirectResponse
 
 from devplacepy import stealth
 from devplacepy.constants import DEVII_GUEST_COOKIE
-from devplacepy.database import get_int_setting
+from devplacepy.database import get_int_setting, mark_notifications_read_by_target
 from devplacepy.seo import base_seo_context, site_url
 from devplacepy.services.manager import service_manager
 
@@ -77,6 +77,8 @@ def _owner_from_request(request: Request):
 @router.get("/")
 async def devii_page(request: Request):
     user = get_current_user(request)
+    if user:
+        mark_notifications_read_by_target(user["uid"], "/devii")
     seo_ctx = base_seo_context(
         request,
         title="Devii",