feat(kb): POST /api/admin/kb/articles/ai-draft endpoint

Generates a full KB article (content + summary) via LiteLLM given a
title, optional category name, and optional topic hints.

- Prompt instructs the LLM to produce markdown-formatted body (300-500
  words) followed by ===SUMMARY=== delimiter and a ≤200-char summary
- Falls back gracefully if LLM omits the delimiter: derives summary from
  the first non-heading sentence
- Charges kb_article_draft feature credits against the admin's account
- Route is /api/admin/kb/articles/ai-draft (POST) — must be registered
  BEFORE /api/admin/kb/articles/{id} so the literal segment wins

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/users/src/handlers/kb.rs

@@ -3,7 +3,7 @@ use axum::{
     extract::{Path, Query, State},
     http::StatusCode,
     response::IntoResponse,
-    routing::{get, patch},
+    routing::{get, patch, post},
     Json, Router,
 };
 use contracts::auth_middleware::AuthUser;
@@ -31,6 +31,7 @@ pub fn admin_router() -> Router<AppState> {
             patch(admin_update_category).delete(admin_delete_category),
         )
         // Articles
+        .route("/articles/ai-draft", post(admin_ai_draft_article))
         .route("/articles", get(admin_list_articles).post(admin_create_article))
         .route(
             "/articles/{id}",
@@ -955,6 +956,98 @@ async fn admin_delete_article(
     }
 }
 
+// ── POST /api/admin/kb/articles/ai-draft ─────────────────────────────────────
+// Generates a full KB article draft (body + summary) from a title and optional
+// topic hints. Admin reviews and saves with the normal create/update endpoints.
+
+#[derive(Debug, Deserialize)]
+struct AiDraftArticleBody {
+    title: String,
+    category: Option<String>,
+    topic_hints: Option<String>,
+}
+
+#[derive(Debug, Serialize)]
+struct AiDraftArticleResponse {
+    content: String,
+    summary: String,
+}
+
+async fn admin_ai_draft_article(
+    auth: AuthUser,
+    State(state): State<AppState>,
+    Json(body): Json<AiDraftArticleBody>,
+) -> impl IntoResponse {
+    let category = body.category.as_deref().unwrap_or("General");
+    let hints = body.topic_hints.as_deref().unwrap_or("");
+
+    let prompt = format!(
+        "You are a technical writer for Nxtgauge, a multi-vertical marketplace platform \
+         connecting job seekers, professionals, companies, and customers.\n\n\
+         Write a clear and helpful help center article.\n\
+         Title: {title}\n\
+         Category: {category}\n\
+         {hints_section}\
+         Requirements:\n\
+         - Write in plain, friendly language aimed at non-technical users\n\
+         - Use markdown: ## for section headings, **bold** for key terms, numbered or bullet lists where helpful\n\
+         - 300–500 words total\n\
+         - End with a short 'Need more help?' paragraph directing users to contact support\n\n\
+         Return ONLY the article body in markdown. Do NOT include the article title at the top.\n\n\
+         After the article body, add this exact delimiter on its own line:\n\
+         ===SUMMARY===\n\
+         Then write a 1–2 sentence summary (under 200 characters) suitable for search results and previews.",
+        title = body.title,
+        category = category,
+        hints_section = if hints.is_empty() {
+            String::new()
+        } else {
+            format!("Additional context: {hints}\n")
+        },
+    );
+
+    let outcome = crate::ai_credits::call_litellm_and_charge(
+        &state.pool,
+        auth.user_id,
+        "kb_article_draft",
+        None,
+        None,
+        &prompt,
+    )
+    .await;
+
+    match outcome {
+        Ok(outcome) => {
+            let raw = outcome.result.trim().to_string();
+            // Split on ===SUMMARY=== delimiter; fall back gracefully if LLM omits it
+            let (content, summary) = if let Some(idx) = raw.find("===SUMMARY===") {
+                let body_part = raw[..idx].trim().to_string();
+                let summary_part = raw[idx + "===SUMMARY===".len()..].trim().to_string();
+                (body_part, summary_part)
+            } else {
+                // No delimiter — derive a short summary from the first non-heading line
+                let first_sentence = raw
+                    .lines()
+                    .find(|l| !l.trim().is_empty() && !l.trim().starts_with('#'))
+                    .unwrap_or("")
+                    .trim()
+                    .trim_end_matches('.')
+                    .to_string();
+                (raw, format!("{first_sentence}."))
+            };
+            (StatusCode::OK, Json(AiDraftArticleResponse { content, summary })).into_response()
+        }
+        Err(e) => {
+            tracing::error!("admin_ai_draft_article failed: {}", e);
+            (
+                StatusCode::BAD_GATEWAY,
+                Json(serde_json::json!({ "error": "AI draft generation failed", "detail": e.to_string() })),
+            )
+                .into_response()
+        }
+    }
+}
+
 // ── Helpers ───────────────────────────────────────────────────────────────────
 
 /// Map target_roles array to a single frontend role label