fix(auth): reconcile role/ban from DB, revoke sessions, fix pin/comment bugs

H1: AuthUser now JOINs session→user and sources role/ban/event from the live
DB row instead of trusting JWT claims. Bans take effect on the next request;
demotion/promotion is immediate. Adds Session::find_auth_context and rejects
tokens whose sub/event_id disagree with the session row. This also closes M2
(banned export) and M3 (banned edit/delete) globally — banned users can no
longer pass the AuthUser extractor.

Adds Session::delete_by_user_id and revokes all of a user's sessions on
ban_user, set_role, and reset_user_pin so existing JWTs die immediately.
ban_user also emits a user-banned SSE for forced client logout.

H9: reset_user_pin used a non-existent column pin_failed_attempts (runtime
sqlx, so it 500'd in prod). Corrected to failed_pin_attempts — the only
account-recovery path now works.

C4: LightboxModal posted comments to /comment (singular); backend only
registers /comments. One-character route fix re-enables the comment feature.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/handlers/host.rs

@@ -9,10 +9,21 @@ use crate::auth::middleware::RequireHost;
 use crate::error::AppError;
 use crate::models::comment::Comment;
 use crate::models::event::Event;
+use crate::models::session::Session;
 use crate::models::upload::Upload;
 use crate::models::user::UserRole;
 use crate::state::{AppState, SseEvent};
 
+/// Revoke all of a user's sessions (best-effort). A failure here is logged but
+/// never fails the surrounding admin action — the live-role/ban reconciliation
+/// in `AuthUser` is the authoritative gate; revocation is defense-in-depth.
+async fn revoke_sessions(pool: &sqlx::PgPool, user_id: Uuid, action: &str) {
+    match Session::delete_by_user_id(pool, user_id).await {
+        Ok(n) => tracing::info!(target_user_id = %user_id, revoked = n, action, "sessions revoked"),
+        Err(e) => tracing::warn!(error = ?e, target_user_id = %user_id, action, "session revoke failed"),
+    }
+}
+
 // ── DTOs ─────────────────────────────────────────────────────────────────────
 
 #[derive(Serialize, sqlx::FromRow)]
@@ -120,6 +131,14 @@ pub async fn ban_user(
     .execute(&state.pool)
     .await?;
 
+    revoke_sessions(&state.pool, user_id, "ban_user").await;
+
+    // Tell the banned user's online devices to log out immediately.
+    let _ = state.sse_tx.send(SseEvent::new(
+        "user-banned",
+        serde_json::json!({ "user_id": user_id }).to_string(),
+    ));
+
     tracing::info!(
         actor_user_id = %auth.user_id,
         target_user_id = %user_id,
@@ -201,6 +220,13 @@ pub async fn set_role(
         .bind(auth.event_id)
         .execute(&state.pool)
         .await?;
+
+    // Force a clean re-auth so the new role can't be cached client-side and so
+    // any in-flight tokens carrying the old role are invalidated. The live-role
+    // reconciliation in AuthUser already prevents privilege escalation, but
+    // revoking is cheaper to reason about.
+    revoke_sessions(&state.pool, user_id, "set_role").await;
+
     tracing::info!(
         actor_user_id = %auth.user_id,
         target_user_id = %user_id,
@@ -263,7 +289,7 @@ pub async fn reset_user_pin(
     sqlx::query(
         "UPDATE \"user\"
          SET recovery_pin_hash = $1,
-             pin_failed_attempts = 0,
+             failed_pin_attempts = 0,
              pin_locked_until = NULL
          WHERE id = $2",
     )
@@ -272,6 +298,10 @@ pub async fn reset_user_pin(
     .execute(&state.pool)
     .await?;
 
+    // A PIN reset must invalidate existing sessions so a compromised/old token
+    // can't outlive the reset.
+    revoke_sessions(&state.pool, user_id, "reset_user_pin").await;
+
     // Notify the *recipient* device(s) if they happen to be online so they can clear
     // their cached local PIN. They'll save the new one on the next /recover.
     let _ = state.sse_tx.send(SseEvent::new(