fix(SEC-REVIEW-3): Add @MaxLength to SearchQueryDto.q for consistency

All other search DTOs (SemanticSearchBodyDto, HybridSearchBodyDto,
BrainQueryDto, BrainSearchDto) already enforce @MaxLength(500) on their
query fields. SearchQueryDto.q was missed, leaving the full-text
knowledge search endpoint accepting arbitrarily long queries.

Adds @MaxLength(500) decorator and validation test coverage.

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

apps/api/src/knowledge/utils/markdown.ts

@@ -1,9 +1,12 @@
+import { Logger } from "@nestjs/common";
 import { marked } from "marked";
 import { gfmHeadingId } from "marked-gfm-heading-id";
 import { markedHighlight } from "marked-highlight";
 import hljs from "highlight.js";
 import sanitizeHtml from "sanitize-html";
 
+const logger = new Logger("MarkdownRenderer");
+
 /**
  * Configure marked with GFM, syntax highlighting, and security features
  */
@@ -199,8 +202,8 @@ export async function renderMarkdown(markdown: string): Promise<string> {
     return safeHtml;
   } catch (error) {
     // Log error but don't expose internal details
-    console.error("Markdown rendering error:", error);
-    throw new Error("Failed to render markdown content");
+    logger.error("Markdown rendering error:", error);
+    throw new Error("Failed to render markdown content", { cause: error });
   }
 }
 
@@ -225,8 +228,8 @@ export function renderMarkdownSync(markdown: string): string {
 
     return safeHtml;
   } catch (error) {
-    console.error("Markdown rendering error:", error);
-    throw new Error("Failed to render markdown content");
+    logger.error("Markdown rendering error:", error);
+    throw new Error("Failed to render markdown content", { cause: error });
   }
 }