feat(core): dynamic custom frontmatter fields for CTF writeup metadata

- Add extra_fields JSONB column to documents table (migration 0003)
- CreateDocInput/UpdateDocInput: extraFields?: Record<string, string>
- parseFile: extracts non-standard frontmatter keys as extraFields
- stringifyFile: writes extraFields dynamically to YAML frontmatter
- toMeta: spreads extraFields from DB row into DocumentMeta
- DocForm: '+ Add field' UI for content creators to add any metadata
- API routes: splitPayload() separates standard vs custom fields
- Doc page: CustomFieldBadges dynamically renders any custom field
- Add db:migrate / db:push scripts + deploy workflow migration step
- Add CTF writeup template (content/writeups/ctf/template/)
- Add sample DEF CON writeup with event/challenge/category/difficulty/points
- Add @tailwindcss/typography for table rendering (prose classes)
- Add remark-gfm for GitHub Flavored Markdown table parsing

packages/db/src/schema.ts

@@ -43,6 +43,10 @@ export const documents = pgTable(
       ),
     createdAt: timestamp("created_at", { withTimezone: true }).notNull(),
     updatedAt: timestamp("updated_at", { withTimezone: true }).notNull(),
+    // Dynamic custom metadata fields (JSONB) — e.g. CTF writeup fields
+    // (event, challenge, category, difficulty, points). Content creators
+    // add arbitrary key-value pairs that are rendered as dynamic badges.
+    extraFields: jsonb("extra_fields").notNull().default(sql`'{}'::jsonb`),
   },
   (t) => ({
     searchIdx: index("documents_search_idx").using("gin", t.searchVector),