Add labeled file materials with format badge

- Store human-readable label in LessonFile.name via optional label field on upload
- Add PATCH endpoint to rename existing files inline
- Admin: label input before upload, click-to-edit inline rename
- Student: colored format badge (PDF/DOCX/XLSX/ZIP/etc) replaces paperclip emoji

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

src/app/(student)/courses/[slug]/lessons/[lessonId]/page.tsx

@@ -8,6 +8,7 @@ import { LessonContent } from "@/components/student/lesson-content";
 import { LessonCompleteButton } from "@/components/student/lesson-complete-button";
 import { HomeworkSection } from "@/components/student/homework-section";
 import { LessonComments } from "@/components/student/lesson-comments";
+import { FileFormatBadge } from "@/components/shared/file-format-badge";
 
 interface Props {
   params: Promise<{ slug: string; lessonId: string }>;
@@ -123,7 +124,7 @@ export default async function LessonPage({ params }: Props) {
                 className="flex items-center gap-3 px-4 py-3 text-sm transition-colors hover:[border-color:var(--foreground)]"
                 style={{ border: "2px solid var(--border)" }}
               >
-                <span className="text-lg">📎</span>
+                <FileFormatBadge url={file.url} />
                 <span className="flex-1 font-medium">{file.name}</span>
                 <span className="text-xs" style={{ color: "var(--muted-foreground)" }}>
                   {formatSize(file.size)}