feat: add leaderboard router, gamification backfill, and shared content creation helpers

Introduce a new `/leaderboard` endpoint ranking top 50 members by total stars, wire it into the app router and documentation. Implement `_backfill_gamification()` in `database.py` to compute XP/levels for existing accounts from prior posts, comments, votes, and follows. Extract `is_owner()`, `create_content_item()`, and `detail_context()` into `content.py` to centralize content creation, reward awarding, mention notifications, and attachment linking. Update comment creation/deletion in `comments.py` to use `award_rewards()` with `XP_COMMENT` and the new `is_owner()` helper. Add shared template partials documentation for vote bars, star buttons, post headers, and topic selectors to `AGENTS.md`.

devplacepy/routers/follow.py

@@ -3,7 +3,7 @@ from datetime import datetime, timezone
 from fastapi import APIRouter, Request
 from fastapi.responses import RedirectResponse
 from devplacepy.database import get_table
-from devplacepy.utils import generate_uid, require_user, create_notification
+from devplacepy.utils import generate_uid, require_user, create_notification, award_rewards, XP_FOLLOW
 
 logger = logging.getLogger(__name__)
 router = APIRouter()
@@ -30,6 +30,7 @@ async def follow_user(request: Request, username: str):
     })
 
     create_notification(target["uid"], "follow", f"{user['username']} started following you", user["uid"], f"/profile/{user['username']}")
+    award_rewards(target["uid"], XP_FOLLOW)
 
     logger.info(f"{user['username']} followed {username}")
     return RedirectResponse(url=f"/profile/{username}", status_code=302)